Can you confirm that your WordPress and PHP versions are up to date?
WordPress version is current.
PHP version: 7.3.24
I know that is not the most current version of PHP, but it has not changed recently and this issue with the theme styles not loading is quite recent.
You might want to try clearing your cache and reinstalling the WordPress.
Deleting all plugins via FTP finally did the trick. I am now slowly re-installing them one by one.
Note: I had already deleted plugins via the Dashboard, but when I accessed FTP I could still see the folders.