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.

In my experience the biggest problem with large groups us the amount of time it takes for combat rounds. Compound that with people being distracted while online, and I think 6 players will be a bit much. If you have everyone prep their turn, and streamline the enemies' turns, it might be ok.

I'm currently running with six. It is manageable and still fun, but I would not add another. 4-6 seems to be the sweet spot.

With six, you do have to make an effort to ensure that everyone is being included. To speed combat up, I make sure to let the next player know when their turn is coming up next so they can prepare.

For my in person game, six is ideal because typically a rotating cast of two can't make it each week and then I can DM for four, which is the best number to actually have at the table.

In my experience, 6 players is doable but pushing it. Turns take a long time, and balancing is hard because there is so much overlap in strengths and they can focus so much damage that significant monsters/enemies don't stick around very long unless you fudge their health pools.

6 can be done but it gets difficult for everyone to feel heard. I often times had to specifically ask everyone what they were doing in non combat scenarios, otherwise it was easy to blast past them. Some people also hog the spotlight.

5 has always been my favorite number personally. It allows for a lot more interesting dynamics, players can break off into small groups to have more intimate conversations without leaving one person alone. Also from the standard Tank+Dps+Caster+healer it allows there to be a wildcard as well.

I've ran many games with 6 people, several with 8. It's definitely doable, and you need to find a way to involve everyone. It helps if you take the 'you do that thing' mentality, which is where don't fight them too too hard of they want to do something, like adding a lot of checks and such to show them down. Keep it flowing, and you'll need to use the 'well what do you think player-who-is-quiet'.

My group had 6 for a campaign and it was a bit of a slog, but once we found a good rhythm it ended up being really fun. We set some ground rules, especially for combat, where you had to be prepared and we'd set a time limit for turns. It kept the game rolling and kind of added a sense of urgency, which was an unexpected bonus. Plus, our DM was pretty lenient on things to let the game flow. He said he'd rather let some small things slide for the sake of time.

We also prioritized having a face character for non-combat situations and kind of had a buddy/group system when it came to exploring, looting, etc. That way you're dealing with less instances of decision making that could potentially slow the game down.

As long as players stay engaged while it isn't their turn and are prepared for their own, it should run smooth albeit a little slower. We had a couple players that were not super experienced and sitting down to explain the flow and order of things before hand helped them find their rhythm.

One added bonus of more people is that the excitement level increases in high intensity situations. It's cool when someone rolls a nat20 with 2-3 other players, but it's even more exciting when a table of 6 jumps up from an awesome roll or whatever.

Have fun and good luck!

6 is doable but I find i have to spend more conscious efforts ensuring everyone stays engaged. It can be easy to zone out or feel left out when 5 other people have things they want to accomplish. If you feel like you can have a good effective zero session where you talk through your thoughts on the larger group to make sure everyone is aligned it should be ok... I could imagine with 6 randos it might be a challenge, but idk, I've always played with friends in-person or online so take my perspective with some grains of salt :P.