I can confirm that MitID login flow is currently broken in Vanadium: the MitID app itself works but when control is back to Vanadium, it does not redirect to the post-login page.
I could reproduce this when trying to login in mitid.dk and when trying to login in my bank app. Switching default browser to either Firefox or Chrome fixed the issue.
I tried to relax every possible setting in Vanadium but I could still not make it work.
Note that I am 100% certain that Vanadium used to work months ago. In fact, to login to my bank app I was forced to change default browser from Firefox to Vanadium because with Firefox it always got stuck in the post-login phase, in a similar way that it is happening now. Now the situation has reversed.
I am not quite sure if this is due to something changing in Vanadium, or due to the changes that happened with the MitID login flow when the barcodes were introduced. It used to be that you could login by entering your name and manually switching to the MitID app to authenticate; now you are forced to push the button to open the app from the login form. This change might have been the one that stopped working in Vanadium for whatever reason. I'm inclined to say that either way, this is a Vanadium bug.