We have very different sleep. For me: I get about 1/8 deep and almost always exclusive to the first half of the night. (Apple tracked sleep pattern that seems common anecdotally; I haven’t checked if a general sleep pattern in studies.)

Only thing I’ve noticed that increases deep sleep reliably so far has been, and I apologize if this feels rude, but it is relevant, is having had sex directly before. (Which is a great reason for it! :)

That said, as you can see, you’ve got much more atypical sleep.

Not an expert here. But I’d try recording yourself and seeing what’s going on at night. (I know there are audio apps for this, maybe video as well.)

If you can rule out snoring or not breathing (blood oxygen readings may help there) you can start looking at things like what you are, ambient noise, etc.

There are also drugs that help with sleep maintenance vs offset. And I know of at least one that purportedly doesn’t disrupt deep sleep. (A common problem with sleep drugs is they also disrupt sleep itself; but there do seem to be a few good ones out there.)