My father (boosted, 72) has covid. he is now on day 8. he is asymptomatic since day 2, only had a low fever as symptom and it stopped. his oximeter is now 91-92 though. 3 days ago it was 92-94. he has apnea. can it be a cause of concern? what to do?

Hard to objectify. If home device, is oximeter accurate? Is the apnea due to sleep apnea? Does he use CPAP device? Is he having struggles breathing, or does he seem relaxed? Check with your doctor regarding potential oxygen supplementation, and potential complications. Since he seems to be on the mend, maybe there is little cause for alarm.

Monitor breathing and temperature, repeat the reading. If it is still 91, please follow up today with a physician. If there is shortness of breath, please see the Emergency room. Pulmonary embolism should be considered. A cardiac evaluation is also recommended. The test may have been positive early in the course and the illness may be prolonged.