At the risk of wading in at an unwelcome point in the thread I'll share my observations from our April 6 sailing on Regatta. Please note that we didn't develop covid on the ship (though many, many did) we didn't test positive until one and two days later after we drove home from the pier.
What I observed onboard was:
Positive cases were isolated in their cabins (it may be that quarantine cabins were filled first, I have no way of knowing for certain). Quarantine cabins were quite easy to spot since each received some sort of tray stand or table outside the room for food delivery. Crew (medical) in "bunny suits" could be seen entering / exiting rooms very occasionally.
As for level of service, I don't really know first hand, but here's what I observed on deck 8, in the penthouses: The butler brought food by the tray with all of the usual set up including a table cloth, this was left outside the door. A call was made to alert the passengers that their meal had been delivered the process was reversed for tray collection. Our butler was reluctant to talk about covid, protocols or procedures but confined that his duties included providing door side service to passengers who had tested positive.
Friends we met on board who had members of their parties isolated elsewhere described a similar system for passengers in other categories HOWEVER the reality is, you still have your butler, (s)he remains responsible for you in quarantine and it's easy to imagine that the standard of service is higher than elsewhere on the ship. I'm not suggesting this is okay, acceptable or something to celebrate, only that the extra person assigned to provide services to this part of the ship surely equates to somewhat more responsive service.
More generally, Oceania and Regatta in particular did a completely lousy job managing the large outbreak on our sailing leading to a variety of complaints. There was zero communication about the ongoing situation much of which you can read about in the "50 cases" thread.