Yeah, I noticed that as well. No 32-bit 3.10-staging which means if you are creating a virtual drive you can't initially select Wine 3.10-staging.
At least you can select another version and then switch to it later.
I tested a game this morning in 64-bit 3.10-staging and it works fine.
Quote from booman
Could it be that the 32-bit 3.10-staging will be released very soon? When I select other staging versions from Wine 2.x or 3.x the staging tab isn't available. When I select the Wine 1.9.23-staging the Staging tab is available. Is it possible to modify an existing 32-bit wineprefix into a 64-bit one?
What happens in a Wine staging is that the a DLL file is redirected to enable the CSMT (command stream multi-threading). In stead of using the wined3d.dll, the wined3d-csmt.dll is used. See https://wiki.winehq.org/Wine-Staging_DllRedirects "Wine-Staging DllRedirects". In Wine 3.2-staging this has already been applied in the registry.