I usually put together my own walking tour of buildings when we visit a city but due to the short daylight hours in December I thought it would be more time effective with a guided tour.
I have learned a lot of what Budapest has from this 2020 posting https://community.ricksteves.com/travel-forum/hungary/walking-to-see-architecture-budapest
but I was writing to see if anyone knew/experienced a tour recently. I'm looking for a approx. half day tour around 150E for two.
I am planning on taking the Franz Liszt tour and wandering in the lobby of the Gresham Palace until the Four Season asks me nicely to leave.
I had an architect friend in town a few years ago and she did a tour wiht these guys and enjoyed it: https://ga-budapest.net/en/ Tours by architects no less. That old post you referenced has a great list of do it yourself visits. Thank you for digging that one back up.
And here is another list: https://www.offbeatbudapest.com/budapest-city-guide/best-architecture-highlights/
And, I called a friend for a recommendation and got this: https://lovefromhungary.com/tours/budapest-art-nouveau-walk/ I took a look at a few of the buildings on her tour and she is indeed getting you off the tourist trail to some degree (in a very good way). If you use her, please post a review here.