I recently had a problem with OVH, one of my disks had to be changed (they didn't ask if I wanted to perform a backup before).

After that, I tried to boot the hard disk instead of the rescue mode, from there I get another email citing another problem with the GRUB configuration. (screenshot below):

Apparently I will have to mount all my disks again and fix this "GRUB problem" caused by OVH.

Unfortunately I didn't find anything consistent and reliable on the internet on how to do this without losing the files on the server.

Any help will be welcome.

Wireguard is now in bionic-updates.
PPA+dkms no longer required for bionic users.

Apparently, there was an official announce by Jason Donenfeld (author) on the mailing list on the next day : Aug 3, 2020.

You can safely remove the PPA config from /etc/apt/sources.d/ if you were previously on it on the supported OSes.
https://lists.zx2c4.com/pipermail/wireguard/2020-August/005737.html

Hi folks,

At long last, Ubuntu now supports WireGuard on releases 20.04, 19.10,
18.04, and 16.04, which means we've got all currently supported LTS
releases covered. For that reason, we're in the process of sunsetting
the PPA that previously provided packages to some users. This email
details possible changes users might consider.

The right way to install WireGuard on Ubuntu now consists of a single
command:

$ sudo apt install wireguard

This "wireguard" package will automatically pull in either one or two
packages with it:

1) wireguard-tools: this will always be pulled in and provides wg(8)
and wg-quick(8).
2) wireguard-dkms: this will only be pulled in if your kernel doesn't
already come with WireGuard.

As suggested by (2), most Ubuntu kernels now come with WireGuard out of
the box, even older releases, to which WireGuard has been backported.
This is great news and will result in much better reliability during
upgrades, as well as smoother compatibility with SecureBoot.

--snipped--

As a very good general recommendation for people new to wireguard ,
USE https://github.com/Nyr/wireguard-install/ (read the README first)

I have reviewed nyr's wireguard-install script and I am satisfied that it is well done.
I compared it with a manually configured wireguard tunnel, and all the defaults seem sensible.
Anything that saves you time should be welcomed.
Shoutout to @nyr, a long time LET/S MVP.