I think it is more common than people realize. If the house has a spare bedroom and the couple is a bit older, there's a pretty good chance they sleep separately at least some of the time. I think movies and shows give people unrealistic ideas about a lot of stuff, including this notion that couples must always sleep together or "something is wrong".
I come from a family of very active sleepers. Spouses quickly understand how sleeping in different beds can be a good thing. The love is still there, but so is a good night's rest.
It could be the aro in me talking, but I don't really understand how people can get good sleep in the same room as one another, let alone the same bed. Having someone within the immediate vicinity, even an extremely liked and trusted person, seems like it would be a distraction at best and at worst cause anxiety over if I was making it harder for them to sleep
Id say as someone who enjoys sleeping in the same bed (often with people who i am in a non-sexual relationship with and sometimes in a bed not designed for two people) it has kinda the same effect that cuddling with a person(sometimes it is just that) for a very long time so it just feels nice and has you rested in a completely different way. I do agree that the sleep quality often suffers a bit so i wouldn't likely want to sleep like that every night.
It is kinda how many mammals have evolved to sleep, ever seen cats sleep in a big ball in weird positions over eachother?
Cold woman under blanket trying to snuggle hot man with no blanket while her cat wakes you up every night jumping around on the damn bed because he heard one of your rustle for 5 seconds.
My sleeping accessories are two cats, I don't have an option in it so no one else does either. Come to visit? Welp you might have 30lbs of dead weight on ya for awhile.
Years ago, I slept on my side curled up like I've just witnessed a horrible murder (still do), and the person I shared a bed with was only 5'4/163cm, and slept with their legs elevated, making them effectively shorter. Three dogs and a cat also shared the bed with us, an American queen sized bed.
We turned the bed sideways, used mattress toppers on each of our sides, and that created a spot in the (now much wider!) middle that was shorter than the rest of the bed. Affectionately named the Bed Trench, it was the new home of the pets.
It definitely takes some getting used to, but it's 110% worth the improvement to quality of sleep. If your apnea is mild you may be able to get an oral appliance instead, and I hear those are more comfortable.
I prop myself in place with so many highly specific pillows I think I'm trying to replicate sleeping in zero-g, with no excessive weight on any part of my body