Enable Mirror Mode. Disable Mirror Mode. Double click a layer to open Layer Attributes. Closing Layer Attributes enables Mirror Mode again... annoyingly.
Also, is there a way to disable Layer Attributes altogether? Accidentally double clicking a layer is easy to do (well it is for me) and having to deal with the panel popping up is a pain.
Painter 2023 (and all previous versions) Windows 10 (Doesn't occur on MacOS)
In fact, it may be that closing any window re-enables Mirror Mode if it had previously been enabled.