Try a restart of psa service. In most of cases solve the problem!
It is recommended to restart mysqld service first, then psa.
Also check on Plesk Control Panel at Updater and be sure that all things (modules, services etc.) there are green colored!
If problem exists, go to root/psa dir and through ssh install the previous version 8.0.0 with --force option.
After this update again through the updater to the most recent 8.0.1.
Remember the 8.0.1 is a final , and will be kept for very long time, i presume,and all the bugs issues from mother 8.0 have patched succesfully!
And please do this: find your psa dir (mine is at /usr/local/psa ) look for /admin/conf/php.ini , it is the PHP master configuration file support for Plesk, and change if it is not like this
safe_mode = Off
most of problems we found in Plesk, like yours, were because safe_mode were on there after upgrade to 8.0
Fix it, and then restart psa.