The best name for this that I’ve seen is “Selective Sync.” Syncthing does not support that natively.
I did propose a clunky workaround: Idea: Workaround for Selective Sync .
While I do not speak for the developers and maintainers of Syncthing, they’ve said before that they aren’t interested in developing a feature like this.
Personally, I’m finding that Tailscale Drive works really well for me, and I’m on the free “Personal” license. I do recognize that Tailscale is not for everyone.