I'm booked on this trip late Oct 2022. The first leg of my flight home is Cairo to Munich (Egyptair) then Munich to Denver (united). I booked on Egyptair to avoid the fake business class seats offered by the European carriers.
Twice in the last few weeks, the Cairo-Munich leg on Egyptair simply disappeared from my booking. I called United and got it reinstated each time (the first time with a different seat as my original seat was no longer available). I asked why this is happening and they said it was cancelled by Egyptair because of a schedule change. There was no schedule change, so they are just making up something to get me off the phone. In any case, suggest you check your flights regularly on the airline's web site, as I received no email notification about this. I'm now checking it daily.