Modifier keys can be assigned to mouse buttons but pressing more than one at a time does not work! For instance, I can assign Shift, Alt and Ctrl to the three buttons on the MX Master and each can be pressed individually. But pressing two or three at a time does not work.

This works fine in standard Logitech Options but is broken in Logi Options plus.

This is confirmed broken for Lift, MX Master and MX Master Anywhere. It is broken over blue tooth and over Bolt. It is broken for both Windows and M1 Macs.