Preferences and Brushes did not import despite selecting for them to do so on install

Is this the first time you installed the beta version?  Even if not, I susp[ect your are not the only person who has found their brush presets have not been migrated after an update.  You are a Mac user and I am on Windows, so I am afradi you are going to have to do a bit of working out, but I'll help as best as I can.

This shows the file locations of Photoshop assets

https://helpx.adobe.com/nz/photoshop/kb/preference-file-names-locations-photoshop.html

Open Finder and navigate to the following location.

Note this is for the previous version.  If you don't find your brush .abr files here, look in the full release version folders.

Users/[user name]/Library/Preferences/Adobe Photoshop 23 Settings/brushes

Copy and paste to the Adobe Photoshop (beta) brush preset folder.

I hope this helps but I have no way of checking the file path, so shout if still stuck, and we'll get a Mac user to help us out.