beside /etc/php/7.3/apache2/php.ini I also changed /etc/php/7.3/cli/php.ini.
But for the web server with apache2 the first path is the right one, isnt it?
Anyways, unfortunately it produces the same error with both changed.
Did you add the entries to the files or modify the existing entries? Make sure that the entries are only present once per php.ini file.
Also check the .htaccess and .user.ini files in your Nextcloud installation folder. If they contain upload_max_filesize or post_max_size entries, delete them or set the same values as in the php.ini files.
Other than that, I can’t think of anything from the top of my head. If none of the above works, the error has most likely another origin. Maybe some problem in interaction with the external storage or mounted drive. Some caching/timeout problem. I’m not sure…