I got the heroic knight 17 inch bag and it works for the framework 16" with gpu it also allows for another laptop. The charger connect on the bag sometimes is in the way but if you are aware of that it is not a big deal and this a great slim lightweight bag.
You could probably do worse than a Tom Bihn backpack. I’m familiar with an older version of Brain Bag, but all their gear has a very good reputation for durability and long life. They have an optional “Cache” sleeve now, which is probably what you’d want. I imagine the 16" will fit the Framework 16, but I’ve not verified it.
I just got a Goruck GR2 34L and the Framework 16" with the GPU unit on fits to the laptop compartment.