I’m coming at this from a theoretical perspective as I haven’t run it yet, so take my ideas with a pinch of salt…
It seems to me that this just needs the same GM table management skills as you would typically apply in a non-combat scenario. Watch the table, make sure Spotlight is being shared, keep an eye open for people who want to come in but aren’t loud about it.
Keep in mind that, ultimately, a player states an action then makes a roll to see if they succeed or fail. But by default, narrating the result falls to the GM although they may ask the player to do that. This is especially true in combat where the players won’t know the damage thresholds and HP of monsters, or if they have reactions which trigger. So the GM has the reigns at the conclusion of every specific PC action and can ask what the other characters are doing while the action is unfolding,
I think players will also get into the habit of sharing spotlight time in the combat, just like they hopefully do in non-combat scenes. If that is something a table has been poor at in the past, then an upfront conversation about the importance of doing this will probably be very beneficial.
The first session of CR’s Age of Umbra campaign has just dropped on YT so that seems like the one to watch for ‘best practice’ advice right now?