We have several HMI pages with a number of buttons.
to group these buttons I made a frame "menu bar" which is placed on every page.

Now I want to lock these in place, because on every page the buttons are aligned exactly.
If I select a frame on a page, I want to lock the X,Y,width,height to prevent accidental moving.

is this possible in the designer?

I do see two options:

Firstly, you could create a frame, where the menu bar is located in the defined position (use a codesys frameswitch).
The content is located in a smaller area within a second frameswitch.
While the frames doesnt need the menu bar, you dont need to lock them.
(If you don't want other users to edit the menu bar, you could locate the menu bar into a accessible library.)

Secondly, if the first option is not possible, you might overwrite the absolute movement value x and y with a integer. The frame could look different in editor then in the visu.

I totally prefer the first option.