I finally solved the issue, after trying on a third computer.
On both other computers I apparently tried to use the button before updating wordpress, so some bad javascript has remained in the browser cache. I didn’t think of clearing it because it happened on two separate computers, but clearing the cache solved the problem.
Thank you all for your help!
I tried it on two separate computers before and after updating to 5.0.3. Another wp blog I’m hosting works fine (also on both computers).
Initially, yes, there were some problems during the update process (some write restrictions in server configuration, but I fixed those and reapplied the update with no problems), but I didn’t look into it since it didn’t work before the update (at 4.9.something) either. I’ll try reinstalling, maybe that does something.
Thank you!
