As far as I know the SimpleX team adds their servers to the preconfigured list of servers in the app.
So if you host SMP servers for others, you could share their QR code (along with a quick description) in some forum or your own website (I know a hoster of serval private services who also maintains SMP nodes).
For info about hosting such a server, see here.
You can also achieve this with
nvtop
and have a pretty TUI (terminal UI).