If you’re getting an Intel-based Framework 13, it will almost certainly work. If you’re looking at the AMD-based one, I’d give it good odds of working, but less guaranteed. My recommendation would be that if you’re worried, you should try to borrow a recent AMD-based computer from someone else to test.
“A recent AMD-based computer” includes the Steam Deck, BTW (useful if you or someone you know has one, especially since they’re both cheap and highly portable). In the standard gaming mode it will just select one of the displays, but if you go into desktop mode it can drive both the internal display and two external monitors (it works perfectly with my dock for example), and it has just one generation back of the same GPU as is in the Framework 13, so if it works with your setup it’s almost certain that the AMD-based Framework laptops will work as well.