Take with a pinch of salt: I would say I have brass ears at the very best.

Well, Intervals are the fundamentals, you have a great foundation! Keep it up!!!

Majorly stuck on off-beat eighth-note triplets in 6/8, though: how in the heck are you meant to count those things?

Ahhh, do you mean this one: https://www.tonegym.co/space/talk?id=NASZ2448MAR&t=4J724BWI3V7
This post has the whole debate on the validity of these levels, and how to count them...

That one I can do (as you suggest) by thinking in 3/4 (even though you wouldn't feel it that way in a genuine duple metre): it's this one I have trouble with.

I notated that same rhythm in 3/4 (see below)
I would count it like:

| 1 + {2-trip-let} {3-trip-let} | {1-trip-let} 2 {+ trip-let} + |

You can also plug it into musescore or other notation app and listen to how it sounds.

I think that this level is a result of some kind of automation on the part of the developers and was not thought through at all.

It makes no sense in any musical setting I can think of and is very misleading. So good luck!

Great achievement ! Congratulations!!!

Outstanding!

on my birthday! congrats bro!

Outstanding! Congrats!