Is it possible to install Home Assistant on a non-UEFI system (x86_64 obviously)? I have some old laptops here and had thought of using one of those for a standalone HA install (it will be a while before I move my media center over to an Open Media Vault-based system, where I would eventually run HA). I don't have the money to buy new hardware for a while (short of the security camera(s) I'm looking at) so need to make do with what I have.
Not officially, no, but you could install Proxmox VE and virtualize HAOS or just run the docker variant on debian.
Install it in a VM if you want to use HAOS or use the Container install method.