IOS Update

That is correct, running iOS 13.X you can only update to iOS 15.1, 14.4.1 is no longer available. If the app developer has kept the app up to date, it should run 15.1.

Dexcom is always a few OS updates behind verifying that their apps are compatible with Apple updated OS. It appears that you know about the Dexom compatibility tool that shows what they have verified.

Apple doesn't make older OS versions available. I think they should for this reason. Dexcom users can either NEVER update their Apple devices currently OR go ahead with one of Apple's "critical" updates and have to just hope that it doesn't cause a compatibility issue with a Dexcom app.

The newest watch OS8.1 has caused the complication of the Dexcom Follow app to stop working. If this were to happen with an update and affected the Dexcom G6 app or the Dexcom Follow app on an IPhone, it would be a pretty big problem and the person wearing the Dexcom sensor would have to go back to the receiver for BG readings.

Apple needs to make older versions available and Dexcom needs to work faster towards updating their apps for compatibility with Apple OS updates.