Pebble is releasing new watches. The Pebble Time 2 does seams to be launching with screws. Considering that the orginial smart watches of Pebble stills works today, is somewhat of an proof of their longlivety. The OS is now open source which is sort of an safeguard against planned obsolence and respects user privacy. However the new watches are unlreased and unproven as of date, but expected to be low-power but great battery life.
Unawatch is and upcoming sport smartwatch. Marketing it self as sustainable, repairable and upgradeable, but not open source and not the best waterproofing.
There is still pinetime from pine 64 available for purchase from eu store for 66€, two days delivery, including 2 years guarantee and 14 days try or refund legal period, or 30€ from Hong Kong with only 30 days guarantee and two weeks delivery.
I guess you can’t find any watch with such long software support.