It’s not just you, as this came up a few days ago for myself and others reporting it on this forum.
I’ve done everything on my end that one could imagine to be done (factory reset router, hard reset router, port forward, open DMZ - etc). My NAT is Open, and every other game on Xbox can find games quickly, and have no lag whatsoever (unless it’s p2p and host is playing off Taco Bell WiFi...)
Someone mentioned that it could be the result of a new Xbox update, which is the only thing I can see being true and there wasn’t coincidentally a Xbox update released the same day MCC’s matchmaking stopped working for myself and seemingly everyone else runnings into this issue.
Worth mentioning that I can still join friends lobbies no problem (quick too), but when they search they can’t find a game due to me being in their lobby. When they search right after, solo queuing, they find a game in ~30 seconds.
MCC’s matchmaking’s working for some - I’d say most - as it would usually, but some people including myself have been affected to where a game can’t simply not be found (not even a single “Player Found” icon).
If I had to guess, it’s either due to the aforementioned Xbox update released the same day people started running into issues
The MCC flight programs networking changes are coinciding with actual MCC and as a result are messing with people’s ablity to find a game.
Maybe I’m just wrong in general but I’ve looked into this wayyyyy too much.