Steps to reproduce:
There seems to be several problems with Programmable Buttons and Overflow Menu
.1
Try to add Programmable buttons to Overflow menu, the button will not work as a button after if dragged there from toolbar, you just get options for it:

2.
If you try to create a new one by draggin Programmable button from Customize Toolbar, you cant edit the button:

3.
You can only add 1 Progammable button from Customize Toolbar:

Expected behavior:
To work like other buttons inside Overflow Menu
Orion, OS version; hardware type:
Version 0.99.123.3.7-rc, Monterey