Sadly, the behavior in the buffet is not new or exclusive to Celebrity nor is this poor behavior limited to cruising! We have sailed for 25 years and run into this everywhere. As a chef and caterer, I can tell you these things happen all the time. We have always (way before covid) carried our own sanitizer to use after going through the buffet lines and using s & p shakers, etc. (even when dining out at home)
For years the cruise lines have done their best to ask guests to use the wash stations, those so arrogant to think they have no germs to spread just past right by. In March of 2022 we were on a cruise on the Edge, the buffet was served by the staff. Our next cruise in November of '22 the buffet was back to self serve. UGH!
There is always people eating at the buffet, eating while walking around, eating with their fingers in the crowd. It's amazing how poor peoples manners are.