As far as I can tell, this would not be caused by a conflict with multipl mirc.ini files.
If you run mIRC and type the following into the status window and press enter:
/timerflash -o 1 4 flash
and then quickly switch to another application, so mIRC no longer has the focus, does the mIRC app icon flash after a few seconds?
Here on my Windows 11 build 26016, using the last mIRC beta, the flash is working
