I thought vo2 max required outdoor walk/run to get a reading.

Very confused by the downvoting, unless it is just against the tone. I do understand the original incorrect commenters though, They are probably confusing the reverse requirement, that the watch requires a certain level of iOS/phone. I know I’ve done that it the past (got the dependancy between watch and phone the wrong way round).

watchOS 10 requires iPhone XS or later, with iOS 17 and one of the following Apple Watch models: Apple Watch Series 4 Apple Watch Series 5 Apple Watch SE Apple Watch Series 6 Apple Watch Series 7 Apple Watch Series 8 Apple Watch Series 9 Apple Watch Ultra Apple Watch Ultra 2