Have you tried Uiua? Because I was in your position once, trying to grok APL, K, J, BQN but failing repeatedly. But then it clicked when I saw Uiua.
Part of that is because unlike other APL-likes it uses a stack (sort of) and I can't explain exactly how but it made it much easier for me to picture how the data flows from one operation to the next (I have to admit I like concatenative languages a lot so I'm obviously biased here too).
On top of that none of the glyphs are overloaded with monadic and dyadic versions, they're one or the other, which reduces ambiguity a lot when trying to read/write code.
There's lots of other little ergonomic tweaks to it that make it really neat, but those were the big ones for me.
Also worth noting is that it has lots of multimedia support - you can generate pictures, gif animations, sounds. So it's easy to "play" with for fun!
I assumed Uiua was "the same" but this is the first I'm hearing the experience might be different. I will check it out, thanks!
Wait, Uiua is a serious language? At first glance it looks like it's trying to be brainfuck.
I take some issue with the implied suggestion that Brainfuck isn't serious, but that's probably my arts degree talking.
Anyway, under the assumption that I'm correctly guessing what you have in mind when using the words "serious language", Uiua certainly qualifies. The author is very passionate about exploring and discovering "the good parts" of the design space of the array language paradigm, and has put a ton of work into making it accessible and practically useful within the constraints of being an interpreted language that autoformats its source code to at-first exotic looking maths symbols.
This is cool