HTTP 500 after update

I have updated from 3.1.1 to 4.0.1 and after unzipping and overwriting files, I just get a HTTP 500 response on all URLs which I used to open before.
I also can’t access the update page. Just tried to give chmod 755 to all folder and files, but it does not help.

The logs laravel-error and laravel-info don’t show anything new.

Are there any details in the web server error log?

Maybe you need to uncomment this line of code?

Solved it. In case somebody is as stupid as me: I downloaded by mistake from github and thought it’d be the same version as on the website. But in this case it is necessary to run composer install, which I can’t do. So I just took the version from the website and everything is fine now.