True open source products are your best bet. TruNAS and Proxmox are popular options, but you can absolutely set up a vanilla Debian server with Samba and call it a NAS. Back in the old days we just called those “file servers”.

Most importantly, just keep good backups. If you have to choose between investing in a raid or a primary + backup drive, choose the latter every time. Raid will save you time to recover, but it’s not a backup.