nextcloud is broken
Something is going on, there is a big error message saying:
Error
Cannot write into "config" directory!
This can usually be fixed by giving the web server write access to the config directory. But, if you prefer to keep config.php file read only, set the option "config_is_read_only" to true in it. See https://docs.nextcloud.com/server/24/go.php?to=admin-config
Before this message appeared, I was trying to log in.
Nextcloud told me that I hadn't configured 2FA, which I had working for months, and then when I entered with a backup code, it started showing this error mentioned before.