Site error 500 after PHP upgrade

This & the rest of apache errors are either due to you using an old roundcube, or the roundcube seems to be conflicting with some other packages. Suggest upgrade the roundcude: How to Safely Upgrade Roundcube to 1.6.11 on HestiaCP (Security Fix) & Last apt upgrade of roundcube broke it!

Agreed, seems to me as well (localhost failing too). Maybe due to mysql/mariadb as well being offline. Check that once.

Cannot agree more. My current installation is around 1+ year old, and with loads of breaking changes due to the packages in play, I too feel, I will very soon have to do a fresh installation. Only trouble is, me having 80+GB of data, and the pain of setting up the stuff, which can kill 2 days and cause back pain too. lols