I have just been forced for the umpteenth time to update photoshop beta, and I am facing the same issue. If this issue hasn't been resolved why continue to push the update only to mess other people up, please make that make sense adobe 🙄
I did get it to work by deleting the shortcut keys for brush size and it worked. Or you can delete brackets for layer boundaries(which i never use) and put them back for brush size and it seems to work now.
Adobe is sleeping already, its been more than a week and almost all of us are suffering from that issue .. now you see its not a big deal to give just a simple update to resolve tha problem ... but heck yeah we just cant really complaint about it as it's just a BETA.. use the previous 25.10 version anyways
It's a known issue. Open Edit > keyboard shortcuts > Tools and scroll all the way to the bottom, and remove the [ and ] shortcuts from the Layer Boundary commands.
Out of interest, what version are you using? I'm wondering if this was fixed with the 25.12, m.2694 update.
I have a custom shortcut I've set for opening the foreground picker (N, which I reassign from a different shortcut) and it works fine in normal photoshop, but three updates ago in beta, it stopped working. It is still set up and shows that it's been assigned to the custom I set up, but no custom shortcuts are working at all in beta.
This same issue now is happening in the live photoshop 25.11 and it's now messed up my workflow there, too. I cannot access my custom keyboard shortcut.