Error 500 during install on Admin screen

I've installed Akaunting to my own server. PHP is version 8.3, database gets filled. Then, on the third screen, for creating an admin, I run into an issue.
After pressing "next", nothing happens. In my server log I see an error 500. Reading through the forums, I think it might be that the .env cannot be created.

What should I change? Is it a rights issue? But I simply unzipped the installation file, so I figured rights would be correctly set. Or maybe some php file needs execution rights? I'd rather not give everything execution rights or even set it to 777

Owner of the folder and files, is automatically set by Plesk and should be ok. Other sites I'm running work fine, so that can't be the issue either.