is 512mb vps enough for my static stite?

Yes, should be more than enough

I run 3 static sites on a 128MB VPS.

Instead of apache or nginx, just use caddy. Works great.

# free -m
               total        used        free      shared  buff/cache   available
Mem:             128          78           0           1          50          49
Swap:             64           0          64

and about all the talk about debian, ubuntu, bsd, I'm just running the latest Debian 12 on it,

# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 12 (bookworm)
Release:        12
Codename:       bookworm