That's great news, thank you all very much!
I was already afraid at first it was some weird macOS filesystem bug only happening on high sierra and earlier which was never going to be fixed.
In the meantime I have managed to add "both directories" to git (with git add paulbr*). It's funny, now one directory shows up twice when viewing my repo on gitlab.
And this is the message I get when cloning:
warning: the following paths have collided (e.g. case-sensitive paths
on a case-insensitive filesystem) and only one from the same
colliding group is in the working tree:
'[...]/paulbrunngård-springyard/main.ts'
'[...]/paulbrunngård-springyard/main.ts'
What will happen with the two folders in the git repo after the patch?