Setting checkbox to disabled unticks it. The checkbox is a bit buggy

Setting the checkbox that is ticked to disabled unticks it and applies the disabled state. It appears that the :selected and :disabled causes conflicts perhaps?

This is the case with any widget in Axure. The :disabled interaction style shows the default, or unselected state. There is no provision for a “disabled and selected” style/state. You won’t be able to determine or change the selection state of a disabled widget either.

The best workaround is to create a set of specific states and styles with a dynamic panel, creating a dynamic panel state for each sub-state or transition you need.

Set it to selected. On Page Loaded, set an interaction to disable it. It will be disabled and selected.