He might be able to do an at home sleep study. My insurance required that and an overnight pulse oximetry test before one in a proper sleep clinic. It was pretty easy and not all invasive. What you do after that depends on the results. Mine showed no obstruction, but I was randomly dropping into the mid 70s for my O2 sats, so I have supplemental O2 when I'm sleeping until we figure out what's causing it. If there's an obstruction, many people get a c-pap machine, or occasionally surgery to address the cause of the obstruction.

Having your O2 sats dip as low as mine do repeatedly and poor quality sleep is a risk for dementia. I work in memory care, and while we've made improvements in that field, there's no cure. No one wants to live put their last few years in a care setting where evrryone is always declining. If for no other reason than decreasing his chances of dementia, he should schedule an appointment asap. If he needs a specialist, many have longer than normal times for appointments due to the covid backlog.