what do i click in properties to play the beta version of rust on my mac
There is no “beta”. You can access the Betas tab in the Properties menu, and that will allow you to switch to the development branch, or the legacy branch, but there is no “beta” of Rust,which is in alpha.
If this does not answer your question, you’ll need to be more specific about what you want.
i’m presuming you mean “legacy” (the old version of rust) which is in the list as in elix’s reply.
EDIT: Nevermind, appropriate corrections were made.
“beta” is only for legacy version. Just play normal, or right click and go to Properties, Beta tab. Pick the legacy beta. It then install Legacy.