I'm not aware of any major brands that offer account free service. The problem is that a smart device like this is not worth much without some kind of app ecosystem, app stores generally demand accounts, and browsing app stores from a watch is not exactly ideal.

As far as I know, Tizen smart watches can function well on their own after setting up the account once and I believe cloud synchronization is even optional. However, Tizen for smart watches is a dead end, with Samsung getting back to Android Wearable.

There's PineTime (https://www.pine64.org/pinetime/), which is very barebones but open source. Popular firmware, such as InfiniTime (https://github.com/InfiniTimeOrg/InfiniTime) can also be flashed onto several smart watches available on your favourite Chinese import stores (for example: https://github.com/StarGate01/p8b-infinitime for the Colmi P8).