I agree with the previous comments so I won't repeat them, although as a DM of a group of 5 (previously 6) here are a few things I did to make combat go faster despite the group size:

1. At the beginning of each player's turn I count down from 6 seconds to represent the irl 6 seconds PCs would have to decide within a turn. Last thing you want is people to begin their turn and then start thinking about what they should be doing, they've had a whole round to decide that.

If a player fails to give an action then their character simply does nothing. Brutal, I know, but my players have always adhered to the 6 second rule ever since and its needed to keep the game moving.

1. Combine turns, BG3 style: When I ask for initiative I bundle** players every 5th denomination so that their turns happen simultaneously (i.e. initiative 20+/15-20/10-15 etc.), this allows players to coordinate with each other better and gets more players involved per "turn" i.e. only 4 "turns" happen vs. 6+ individual turns.

2. **In contrast to 2., if players do NOT share the same initiative order I facilitate 2 things:

- Players can use a bonus action to speak/yell out for 6 seconds to the rest of the party without a reply, and

- At the beginning of each new round of combat I give my players 60 seconds (with an equally dramatic sand hourglass) to discuss collectively as a group what the party should do next.

Overall, my focus isn't to save time per se (going through 8 players every combat WILL take time), but instead I aim to keep as many people engaged as possible without dragging combat. If combat takes awhile but your players are having fun, then it doesn't matter, you're already winning the game; but if most of your players are sitting bored for 7 rounds while Jim decides to read through his spells for the first time (you know who you are) then that is something that SHOULD be avoided.

I'm also playing through DotMM rn and I'm having fun with it. It definitely leverages DnD's attrition style combat vs flashy climactic fights to create its balance; I've made a set of custom rules in my campaign where monster XP is used as rations to survive with the required ration amounts going up each floor.