It's good that you get the underlying math / strategies—just think of this as a two-level process, and that's only the first level.
The second level is then learning how to apply those concepts in GMAT-format problems...and there's a lot more to learn at that level. So it isn't the case that, after you "get" the first level, you can then just go do all the second level stuff. You still have another level to learn. Think of the OGs as your next lesson, not your "test" to see whether you learned the earlier (book) lessons.
When you go to try the first OG problem, start with a couple of problems from the "medium" level set. You've found your "right" level when you can do some but not all of the problems—so you're not totally over your head but you still have things to learn / improve.
If you realize, nope, none of these are happening right now, then go to the Easier set. Conversely, if they
all feel easy, jump to the Harder list. Everyone has different strengths and weaknesses, so be flexible / work accordingly.
Next, use the concepts discussed in this article to help you
learn from those problems / learn that "second level" that I was talking about.
https://www.manhattanprep.com/gmat/blog ... -the-gmat/Also: Don't just read a solution end to end. Like, never.
When we do that, we're like "Yep, that makes sense, got it"...and then a week or two later, we realize it didn't stick. (And that's part of the reason why you keep struggling with OGs, by the way—the 2nd level stuff isn't sticking due to the way you're studying.)
As you start to read a solution, one of two things happens:
(1) You get it; you feel like you could finish it yourself. As soon as you feel this (or just have any "Ah!" idea / moment),
immediately stop reading the solution. Go do the problem again, pushing yourself as far as you can. If you get stuck, return to the solution, but stop again the minute you get unstuck and go push it as far as you can on your own. (You might do this multiple times for one problem.)
(2) You don't get it. You just keep reading and are like, "I know the meaning of these individual words but I would never think to do that / don't get it." In this case, also stop reading the explanation. The "right" response in future is just to guess and move on—at least for the foreseeable future. As you lift your skills, you will be able to loop back around to some of those kinds of problems and now you get them. But right now, it isn't happening, and there are a ton of other problems that you are partially getting...so go spend your precious study time there.
So basically, in either circumstance, you don't want to continue reading the solution straight through.
Try that for a week, then check back in to let us know how it's going. (Or sooner if you have questions / concerns, of course!)