We just returned from the Quest. You should have at least one formal night per segment if I'm not mistaken. A sports coat with a tie is fine, a suit would be nice. On our formal night, dress was all over the map, including a couple who arrived at the restaurant in shorts and t-shirts who quickly realized they should dine eleswhere.
We flew from LAX to Rome on July 7, masks were recommended both in the airport and on flight. We wore our the entire time unless eating or drinking. I would say about 50% shared our diligence. On board the crew is wearing masks indoors, but very few passages wore them. Seabourn stated that masks were required for tenders and shuttle buses, however there was zero enforcement.
We opted to use eMed for our testing needs. Buy the testing kits before you leave and take them with you. We ordered a few extras in case requirements to re-enter the US changed while we were abroad.(plus if you need to re-test or something goes wrong it's always a good idea to have a few extra) Download the app at home. Then when you need to test follow the instructions on the box, it uses a "zoom" like video call to make it a proctored Covid test. Seabourn recommended this brand and it was very easy to do the tests in our hotel room. Plus you can submit the cost to your health insurance, assuming you are in the US. We were reimbursed for the cost of the tests (minus shipping). We needed to test in Rome on a Sunday and the options were very limited.