I'm not sure why this isn't working in AE Beta, it's working fine for me in AE 2021, but after creating a layer, if I go to open layer settings it's grayed out. It isn't specific to any project file or anything, just in general.
Yeah seeing the same thing here. It should actually change to "Solid Settings..." in the menu, but still says "Layer Settings..." and is disabled along with the keyboard shortcut.
Looks like if you select the Solid footage item in the project panel, accessing it from there still works.
Should be fixed in 22.0x51 which will be on CCD later today.