Eyerolling so hard. I'm not even going to watch the click bait video. Also, I'm not in Texas.
The law in question. Which makes it a crime if an individual
From the Section referenced, said material would be something that
Not included: panty shots, bra shots. Also, note that, from a bit later in 43.21(a),
So I would think there's a fair bit of space to argue just under the 'patently offensive' banner.
Also note that the cops can't just grab your phone or break down your door and demand to see what you've been looking at - they're going to need a warrant. So there's going to have to be some reason to try and enforce this law to start with. Admittedly, if I owned a bookstore, there would probably be some material I might be more concerned about carrying if this law takes effect, but I'm not super concerned about my personal collection.
Finally, consider the number of characters who are at least 18 in manga/anime who are drawn
exactly like characters under 18. Komi-san and her mother come to mind - literally the same character design with different haircuts. If all the characters look to be the same age, and some are certainly over 18 and some are certainly under, this entire exercise becomes so impossibly subjective that it's going to bog down in appeals going back and forth. Not sure that results in a favorable outcome, but there is the broader question of whether the courts really want to be in the business of adjudicating how old all the characters look. I suspect they don't.