Not strictly a recommendation, but Terramaster is a good brand to look at if you want Synology-shaped hardware which can run TrueNAS or Proxmox or any flavour of Linux you want.

Along with various other devices (including a large Synology which I wouldn’t buy today), I run Proxmox on a small two bay+two nvme Terramaster. I have a bare bones Ubuntu LXC running Samba configured for Apple Time Machine, an VM running Scrypyed, and PBS for Proxmox backups. Nothing on it is critical so I don’t bother with any storage redundancy.

I have the F8 Plus, great little unit. It did need a BIOS update when I first got it to enable Proxmox/other OSes to work properly.

Recently replaced the internal USB boot drive with a small NVMe USB enclosure; using a 90-degree USB connector and using a dremel to sand away an opening for the cable to come out so I could mount the enclosure externally.