It is to overwrite the current Linux OS with the one you want. I came across this idea here [0]. I researched and got Alpine Linux running on Hetzner (even they don't support custom images) using a similar method [1].

This seems to be the guide to do the same with Arch Linux [2], I'm not sure though.

Once you do create a successful Arch image on OVH, take a snapshot of the machine before installing anything else, in case you want to start from a fresh Arch image in the future.

[0] https://github.com/elitak/nixos-infect

[1] https://wiki.alpinelinux.org/wiki/Replacing_non-Alpine_Linux...

[2] https://wiki.archlinux.org/title/Install_Arch_Linux_from_exi...