lemmy can run on a decent variety of hardware, just has to be some thing left on 24/7 and exposed to the internet (be careful, the internet is a hostile place… mine was getting scanned and poked constantly until I put it behind cloudflare and then locked the firewall down to just let in cloudflare), and of course more users take more powerful hardware.
For my personal just me instance though, I’m just running it on a Raspberry Pi 4 I run some other stuff on. Uses less than a gig of memory.