Boosting doesn't really work with twinks. Why? Since BFA (?), Blizzard has reduced your XP by 95% if you queue with an XP-locked toon, I think because people were boosting islands with XP-locked 110s.
A lot of people, myself included, thought it might work because it was common in Remix but in Remix most people were using 20 HOly Priests on F2P accounts so they weren't technically XP-locked. In fact, you keep accruing XP, you just don't level. Technically you could escape Pandaria and create an XP-locked toon in Remix but most people didn't do that.
Now if you happen to randomly end up in a group with a twink then you will get normal XP. You just can't queue in the same group. I tried this morning to end up in the same group as my alt and had no success. I queued both as DPS at the exact same time like 8-9 times in a row and our queues never popped simultaenously. Maybe you can get lucky but it's hard to arrange.
It's hard to stay in a group with a twink too because in TW, as of lately anyway, the healer always leaves. This is kind of dumb. They may have "instant" queues but they're not really instant. And what's better, an instant queue followed by a 10 minute clear or a 2 minute wait for a 4 minute clear?
Compounding all this there's a bug that if a full group in the dungeon queues and some unknown condition happens, the queue says "2/3 DPS". It fixes itself in ~2 minutes but you have to explain to people it's a bug, people will try leaving and re-queueing (which doesn't help) or, most likely, the healer will just leave. And if you're a twink queueing as tank (eg Fury Warrior, MW Monk) then you're better off queueing with as few DPS as possible so you may as well leave too.
Oh and that "2/3 DPS" bug has been a thing since at least 8.2. I found reports of the bug from 2019. It could be an anti-twink measure or triggered when the dungeon clears too fast. I really don't know. Some have speculated it's because of instance limits but I'm 99% sure that's not the case, in part because you NEVER see the bug when it's less than a full group.