Sounds like the DM needs to put their damn foot down
I'm awkward and quite bad at that normally but if my players have gone off topic for more than a minute I'll soft remind them to get back on track, another minute or so and I'll bring it up again, and if we've wasted 5 minutes I activate my autist mode and just straight up mention were way off topic once a spot opens, and refocus the game
That's part of the damn job, I can run a table with up to 10 people without too much of an issue as long as everyone actually comes with their GODDAMN CHARACTERS FINISHED, DAVE