Purchasing Apple Watch GPS+ cellular outside of US

I’m thinking of purchasing my next Apple Watch when we go to Europe in September if the SpO2 sensors are still not installed and working on the watches sold here in the US. I currently have a series 9 which was purchased prior to the patent infringement lawsuit, so my watch has the feature and software and I do utilize it and would like to do so with my next watch as well. I have a few questions or concerns though by purchasing the watch outside the US. I always also get AppleCare. And I believe I’m able to purchase that after the fact, so maybe wait until I’ve returned to the states and purchase the Apple care at my local Apple Store? Just so the warranty isn’t valid in the European country it was purchased in. And if the watch had the tech and feature and software capability at time of purchase, and I’m able to use it during my trip, however I then return home and my watch does an update, will I then lose the O2 software capabilities? Such as it will be disabled as they’ve done to others? I understand the technology would still be in the device, however, would the watch still be able to conduct a reading? With Masimos patent not expiring until 2028, that’s just way too long to hold out for another watch and I’ve had an Apple Watch since the original. Thank you for all your info and knowledge in this area.