classic question.
I know most people prefer 4 but I’m running an online game (Waterdeep Dragon Heist) and was curious how bad a six person online game might be?
Nah, you just need to be upfront about what is expected from players during combat.
You need to make it clear that it is up to each player to stay engaged when it is not their turn, little things like cheering their party members go a long way to staying involved when it’s not their turn.
They need to be considering what they plan on doing before it’s their turn. Part of that you the DM can assist with by announcing whose turn it is and who is next.
6 player combat can be a slog if these are not adhered to.
not all players are well seasoned I’m a little worried they won’t be able to do that