These are really good questions.
Basically, it's boring. How to make it not boring? Is it ok in an OSR dungeon crawl to treat the scenes more... well, cinematic - with more frequent spotlight change and faster action resolution? If so, how are described actions played out in the proper spirit of OSR?
Absolutely, yes! Cinematic with fast changes is exactly how OSR works best for me. More generally, actions are
abstract and encompassing: "You dive across the chasm, somersault, and suddenly stab the troll in the belly with your dagger!" is a description of
one action, not three. Be broad, even generous in your cinematic description.
And another question, somehow related to the slow scene progression. Is it ok to not ask for consent (no, not that kind) from everyone when they presumably do something as a group? Like, if someone says "I enter the dungeon", should I ask everyone if they are following or just go to the next scene if no one objects. I usually ask every one what they're doing because I don't want to retcon descriptions if someone changes their mind, but it doesn't do much other than drag things out. What is the OSR way of handling it or is it that my group just doesn't want to be bothered with such matters?
Two things here: first of all, yes, it is fine to ask if everyone is doing what one person declares. Essential, even, to prevent some players from dominating others in many cases. "Is that the group decision?" or "Horvax enters the room, does everyone follow?" are perfectly fine questions and ensure that each player has autonomy and jurisdiction over their own character's decisions.
Back in the day, when groups tended to be larger and table-level consent was harder to come by organically, it used to be that each party established a "caller", which would be that player responsible for communicating to the DM what the entire party is doing (according to some pre-established guidelines, i.e. the "marching order" in which the characters always progressed through the dungeon.) Here "consent" is established by the mechanic, before play begins, and it's up to the players to choose a caller they trust, and to check that caller with their own input as the game plays out.
The second thing is:
you do not need to retcon anything or let players "change their mind"! It's perfectly OK to tell them "too late," and move on to the next player. That said, a well-placed "Are you
sure you want to do that?" can do wonders to avoid attempted takebacks.