We always aim for the MDR on embarkation day - the only day we eat lunch there - we haven't yet cruised post covid, but precovid we always found that the dining room was far less crowded than the Lido, and especially on embarkation day, we've already had enough of line ups . I hope we will be onboard in time for that lunch this time - we changed our flights because of the current airline delays ...
If not the MDR, I would suggest avoiding the Lido if you can - the Dive In, or depending on the ship, there are other lunch options.