Honestly I'd advise against the thinking of "it would have been unproductive for my skill level" - if there's something you're uncertain of how to tackle, the best first step is to tackle it. Not necessarily just because there is always going to be some value in it as practice, but also because it'll help both you better acquaint yourself with the problem in practice (rather than in theory), and it would provide the person giving you advice a clearer example of how you're thinking about it, which is a far better starting point than providing advice in a vacuum.

All that said, you are entirely correct in how you assumed you would approach it - and that's kind of the beauty of the whole focus on cast shadows. No matter how complex the structure is, no matter how numerous the individual forms or components are of a given texture, their only purpose in what we're doing here is to cast a shadow. So similarly to how with hair, many strands will come together to create a lock (a larger form, not particularly structurally sound, but functionally a mass rather than a collection of individual parts), the numerous nature of grass as a texture doesn't actually make more difficult beyond requiring more time and patience.

In terms of complexity it's not really any different from this spongy texture - there are many holes of different sizes - but because we think of it as a single structure, it's less overwhelming. Similarly, grass can be regarded as a single structure with many crisscrossing elements, but ultimately it's still just forms casting shadows, and surfaces receiving them. It's just a little more chaotic is all, but if you look past that, it's the same underlying problem that you've faced many times before.

Anyway, looking at your texture challenge work, as a whole you're doing very well. There are a few things I want to call out, but as a whole you're demonstrating a pretty well developing understanding of how to approach texture per this course. It does however bear keeping in mind that this course isn't concerned with teaching students how to add detail to their work, so at the end of the day we look at this concept through the same lens we look at everything - spatial reasoning. Other courses will explore texture differently, especially if their goal is to teach you how to detail your work, whereas here it's just another excuse to get you to think about the relationships between the forms you're working with as they exist in 3D space.

This actually is something worth keeping in mind when it comes to choosing the textures you're working with. Using Lesson 5 as an example, there are tons of references (for example, ones with open mouths, maybe difficult angles, and other such peculiarities) which may introduce complexities that undermine the exercise somewhat, some references can be more distracting than beneficial. For example, the bubbles force you to contend with a rather different problem than just dealing with different solid forms/surfaces and casting shadows. The translucency of the bubbles interferes both with their casting of shadows, and their receiving of it, and they definitely don't play nicely with our strict black-and-white medium. As a result you end up fussing more with the specifics of that reference, rather than developing your understanding of the spatial relationships involved.

Another point I noticed is that in some cases - like the coral texture - you did a good job of applying something I'd shared with you in your wheel challenge, but this wasn't always the case, as it's not applied in the sponge texture, or the cracked earth. Here's what I had mentioned in that previous feedback:

In all fairness to you, when it comes to those tires with shallow grooves, or really any texture consisting of holes, cracks, etc. it's very common for us to view these named things (the grooves, the cracks, etc.) as being the textural forms in question, which can steer us away from this use of cast shadow shapes - but of course they're not forms at all. They're empty, negative space, and it's the structures that surround these empty spaces that are the actual forms for us to consider when designing the shadows they'll cast. This is demonstrated in this diagram. This doesn't always actually result in a different result at the end of the day, but as these are all exercises, how we think about them and how we come to that result is just as important - if not moreso.

By filling in the holes of your sponge - which ties the cast shadow not to something you can control, but ensures that the shadows are always the physical size of the hole you're trying to represent - you're losing the benefits of working via implicit markmaking. The direct study in the box to the left of that one however does actually demonstrate this being handled better, with the holes not being entirely filled in, forcing you to think in terms of the shadows those 3D structures actually cast.

When it comes to implicit markmaking, it's very easy to end up fixating a bit too much on the kind of result you want to produce, rather than the process that is meant to produce it - and so for example you might end up making a lot of little stray, broken, or dotted lines, as we see in your basket weave, leaf, coral, and to a lesser degree in later textures, but it still comes up on occasion (like the soft tofu). Ultimately it comes down to breaking away from the process of every mark starting out with an outline (where you're designing and enclosing the given shadow shape), and then filling it in as noted here. When you allow yourself to make individual lines freely like that, that closeness to the result is likely to shift you away from thinking about the process and more towards the result.

The diagram from this section of the notes has something to offer in this regard, specifically towards the bottom where it talks about the "lost and found edges", focusing on having those last remnants of cast shadow occurring where forms physically meet, allowing the shadows to get trapped and be protected as the light source gets ever closer. This helps create the result that the viewer's brain is more readily going to use to fill in the gaps. You can also see this in the textured example from the diagram for the leaves exercise - you did this a little in your own attempt, but pretty much every single mark I drew there was a V where two of the leaf's veins were meeting at a junction. The V's then taper off, until a new junction where they grow again. Arguably we can think of this as a continuous cast shadow where in the straightaways, it's either blocked from view by the vein itself, or so small that it's imperceptible.

The last thing I wanted to call out is an aspect of the challenge where, despite handling a lot of this stuff pretty well, you did kind of drop the ball. That is, you kinda forgot that the point of the rectangular section of the exercise is to create a smooth gradient that blends from the solid black bar on the left to the solid white bar on the right. You did a decent job of it in some cases: the basket weave is solid, the bricks do obfuscate the solid edge of the black bar, though much of it is weighted towards the far left rather than being spread out (admittedly that's pretty similar to the demo so I'd consider it fine), and a number of the later ones are similar in this way to the bricks. But it really seems that after the first page or so, the gradient itself became something of an after thought, rather than the driving motivation for focusing on cast shadows (as cast shadows are the only thing that allow us to create this kind of gradient). So, be sure to keep that in mind when practicing this exercise in the future.

All in all, your work is progressing well - just remember to stick to that process detailed in the reminders section, don't forget about the gradient we're working to create, and don't let the individual references dictate the exercise. Always use them as a source of information, rather than the driving force for the whole activity.

I'll go ahead and mark this challenge as complete.