version 1.2 should have dependency 2.1.20 since it breaks the game if you're still using 2.1.7–2.1.19.

I mean you are right, but I shouldn't repost mod with same version number.
I can update it so 1.2.1 have this lock.

i suppose i should have specified 1.2.x
but thank you, i would've done the same :)

I suppose the proper way would also be to delist 1.2.0 so it disappears from the update tab in-game for 2.1.19

The 1.2.0 version is completely fine on the latest experimental branch (2.1.20+) and works without any issues on my end, so delisting it isn't necessary.
These kinds of issues are normal when developing for the experimental branch, where major game changes are expected. My focus is simply on maintaining compatibility with the latest experimental version. I won't be pushing an update just to swap the crash message for a version warning, but thanks for the input!