I didn't see the episode, but I've seen commentary online, that since COVID, on some of the soaps, you rarely seen anyone answering a door because that would be too hard to film with social distancing. So thus, beginning in summer 2020, we started seeing most characters walking into homes they are visiting, without anyone answering the door.
Of course, we have all complained for many years that on various soaps there are random walk-ins, such as the DiMera mansion on Days. But it got worse on all the shows since the need for sets to observe COVID protocols.
Would this ease as more of the actors are vaccinated? But we don't really know who is or is not vaccinated on B&B, Y&R, and Days -- unless an individual actor announces on the actor's social media that he/she is vaccinated. And now with omicron, who knows what will happen with set protocols.
I guess the answer to your question is another question --
Did Deacon enter Brooke's home because:
1) This is an intentional piece of the storyline that she lets him do that, or that she's lax with her home security.
2) This is part of a COVID set protocol.
3) Neither #1 or #2 ... The show got lazy and messed up and didn't realize it would be odd to have a visitor simply walk in.