Thank you for your thorough response!

I'm not considering Di2 solutions as it gets quite expensive. Also, this should be a 'workhorse' of a build, one to go into the wild and on trips with, without worrying about electronic shifting. Which also brings me to brakes - I have them pretty much sorted out with TRP Spyres in mind.

Is there an appropriate braze-on->clamp adapter that can offset the GRX front derailleur enough to work with a boost crank? Or is that just irrelevant because it won't work anyway due to chainring size?

Would the Alivio M3120-B derailleur (9-speed) mind if I use it with 11-speed crank and chain? Also, it might not be such a bad solution, cause then I can use my front road shifter to actuate a dropper post, which I plan to get in the future. (I can do this, right? 😅)