You can try turning on dark mode to make it a little easier on your eyes. It's in settings, some videos look funky but I use it still

This clicked (sort of) for me by thinking of it as an exclusion of all other possible causes. In the case of the example sentence, the ONLY path that Luke has to become a Jedi is via being trained by Yoda, and being trained by Yoda is CERTAIN to make him a Jedi.

Therefore, you can derive information in both directions. If Yoda DOES train him then he will become a Jedi. If he DOES become a Jedi Yoda must have trained him.

This is different from typical logical relations where you are limited in what you can know. For example:

if A -> B, the contrapositive is /B -> /A

If we are given information about /A, we do not know what happens in this case because there is no arrow flowing from it to another thing (to egregiously oversimplify the actual mechanism). But if instead we had:

A <-> B and its contrapositive /A <-> /B

We now know what /A causes, it must mean cause /B, whereas in the first case you would not be able to generate any reliable conclusions.

If two events are inextricably linked, and are the sole causes of one another, the "if and only if" wording applies, and you have this certainty that if one event happens, the other MUST as well (no matter which you start from). This logic also applies after negation.

I'm down, planning Oct

You seem really eager to improve quickly, I think doing many PTs is potentially a way to learn, but doing smaller drills and targeting your areas of struggle is probably a more effective method. I would really spend time reviewing what you got wrong, on the blind reviews. I think you should view PTs as a way to test your knowledge, but they should be supplemented by regular practice too