Confirming this quest chain issue with Myr at Mages Guild is still an issue as of 11-Jul-02204.
Talking to Myr at this step of the quest chain, when you get the "LOOKING_FOR_PRINCESS_OPTION_19_1" option prompt the game completely locks. You can't choose any other options or even escape to menu, and have to force-quit the game.
Only workaround is to revert to an earlier save before you talked to Duncan and choosing the option like "It's strange for an elf to be helping rebellion" to get the chance to interrogate the Elf girl yourself; and then get from her the location of the Princess - which lets you bypass the entire Myr conversation.