I'm running a campaign with 6 players (don't tell me that's too much, I know) and it's impossible for them to focus on the game for more than ten minutes at a time.

Some elaboration is required.

I'll just resort to the standard advice: Talk to the players. Why are they having a difficult time being focused? Ask them if you're boring them or if they perhaps thought there was another form of D&D they were expecting? As in, do they prefer combat or do they prefer roleplaying? Is your voice just too calming and they're falling asleep without a hit of TikTok? 

For a random guess solution: Six players isn't too much. Just keep track and make sure nobody is being left out. If someone has been too quiet for too long pause and ask them if there's anything their character would like to do. Maybe have them all roll initiative and then you go down the line asking each one what their character is hoping to accomplish in the area they're currently in. 

Crank up the stress: If you're playing in person, occasionally roll a d20 behind the screen. Pick a random player and have them roll a random check. Wear a look of concern, roll some more dice behind the screen, throw on an "Oh no!" expression and then calmly say "Ok, thank you" as you jot some random note down. 

It sounds like you got a group that came expecting a game of dungeons and dragons, only to find there are no dungeons and dragons in your game.  But hey, easy fix- just add those elements to your game.  

Get an extremely dangerous dungeon ready for them to crawl though, along with a dragon who has claimed a portion of it as its territory.  That will get them to pay attention.  Trust me. 

Are you playing online? That can cause greater difficulties for distraction when there are other things they can be looking at at the same time. I've played in sessions where some of the players were actually playing video games at the same time.

Not sure if there's an ideal solution for that, but I try to make sure I ask quieter players what their character is doing; it's common for one or two players and their characters to take the lead in various situations, but it's not fair if the time is focused on them with the others just in the background, as they can be doing things as well.

It can also be an issue of pacing; I like to put puzzles in my dungeons, but there's a big risk of the party getting bogged down by them, so I usually have ways to move them forward towards a planned solution, or I try to build a puzzle without a planned solution such that anything they all agree on will work, either way the aim being to make sure they don't get stuck.

Some players get bored by social encounters, others by combat encounters, but in both cases it's usually the same problem; taking too long and wearing out it's welcome, or becoming too repetitive. Combat in particular can run into this easily if a fight just becomes the same turns over and over until it ends, so it's sometimes good to plan for bigger battles to have distinct phases when the enemy changes its tactics, or there's some twist (reinforcements, environment changes etc.). For social encounters like a big party you could give the group opportunities to split up so they can talk to different NPCs, some can sneak about etc.

Take care with letting the party split up though as that can lead to another common problem which is long periods not doing anything because you're resolving a combat for others. It's usually a good idea to plan for ways you can push the group back together, e.g- if the sneaky team gets caught, maybe the whole household is alerted quickly so you can roll the rest of the party into initiative as they respond to the alarm by causing distractions, or rushing to join the fight.