There is one solution I've seen being used to solve this issue.
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.
