Then your user has a shell that is not bash. You could change that with chsh or by editing /etc/passwd directly, but running another shell might break scripts or cronjobs that rely on the shell being whatever it is now, so be sure to test.
Not much, save for bugs.
But for a container, the host should have same or newer kernel version than the guest, otherwise there could be required features missing.
So with an up-to-date host, you have a better chance of a guest upgrade succeeding.
That's the system-wide log. You obviously have /var/log/apache2/error.log.
However, this will only show errors that aren't associated with a vhost. Those logs are in /var/www/vhosts/system/<domain>/logs.
Use smartctl -a /dev/nvme1 or nvme smart-log /dev/nvme1 etc. on the devices and compare the power_on_hours, that should tell you which ones were recently installed :)
(if neither is installed, install smartmontools or nvme-cli)
When you know the new ones, you can build the new raid.
Well, there...
So you got two new devices nvme1 and nvme2?
Next time you have to set up a server, I recommend you use lvm on top of the raid and then create the volumes within lvm.
In such a setup, you can simply extend the lvm volume group adding more devices and then grow the individual volumes and filesystems.
Which version of proxmox do you have?
proxmox 7+ is actually based on debian 11, so it is a lot closer to ubuntu 20 or 22 than to 18.
Updates within a release should be fine either way.
The thing is, Redis and memcache require application support to be useful, while with varnish you'd rather have to take care of not caching things that should be dynamic.
Like setting the browser caching parameters.
First try with other software that doesn't hide the actual problem.
Second, email sending limits are for sending mail from the server. Using Outlook on port 465, you are trying to send mail to the server. Different direction, different filter.
That may be, but the vps host will still use all otherwise unused ram for caching. How exactly it is assigned depends on whether you have a separate device/filesystem for your vps or it lives within the host filesystem. If you have a separate physical device passed through to your vps, there may...
I think you would need to have the hosting set to "Dedicated FPM application" for this to be able to work on a domain-basis at all.
Otherwise that would not be possible as the normal "FPM application served by ..." pool is not unique to the individual domain.
apt-key add plesk.gpg puts the key in /etc/apt/trusted.gpg.d/plesk.gpg. You need to copy or move it to /etc/apt/keyrings/plesk.gpg, as it apparently isn't there yet.