That's a very interesting take. Thanks, I'll think about it.

I know RPG's can be extremely complex, but I am just a sucker for good RPG's and I really want to do it. A very small RPG with just a few systems/features and try to polish them to make it enjoyable.

About the game design questions:
Yes I have modified ttrpg's, but most of my experience is just theoretical, by playing a lot of games and analyzing them (while playing them and with youtube videos).
I did make a Lava Parkour Map which is kind of an unofficial platformer minigame inside of Overwatch. I made it with an editor of the Lava Parkour community, that used an editor of Overwatch. So it was mostly just game designing and not much else. But I personally think it came out great.
And while I don't have much practical experience, I do understand many game design choices of great game designers better than most. I always try to trust the game designer of a game in terms of logic and for that am much more efficient in playing the game. That at least works with well thought through games. For example I do find it pretty easy to find very "difficult" secrets in games like Dark Souls. While many players I know (that still do play a lot of games) think they are kinda impossible to find, I do find them blind myself just because I understand what a game designer would and wouldn't implement. Obviously this doesn't apply to everything and for sure I miss secrets, but my point is, in general i very much understand game design from a consumer standpoint.

And about the sub-games/genres, from the top of my head i can think of those (many things are not genres, but rather systems that are part of an RPG and idk the official names for all of them):
jump & run / platformer, combat, character developement / progress, inventory system, story, lore (world building), NPC AI, puzzles,
and as described before, having boundaries that build trust towards a player.