My proxmox 6 test install locked up every day or two. Here is the fix. This in particular seems to apply to common hardware on Hetzner servers.
In /etc/default/grub, update this line :
Reboot and you should find your server stable.
Read more on the proxmox forum at https://forum.proxmox.com/threads/random-crashes-reboots-mit-proxmox-ve-6-1-auf-ex62-nvme-hetzner.63597/page-2