Is there a way to continue to support devices with a low version than wearos after updating a watch faces on Wear OS 4?
For personal use yes WFS 1.3.13 supports Wear 3.0 API 30 and WFS 1.2 should still support Wear OS API 29 for some other watches.
But you can’t sell them in Play Store.
Wear App Quality Guide
Caution: All apps must target a version between Android 11 (API level 30) and Android 13 (API level 33), inclusive. As of August 31, 2023, apps targeting Android 10 (API level 29) or lower aren’t discoverable from the Play Store on devices that run Wear OS versions higher than your app’s target API level.
Ron
Samsung Developer Relations
The problem is, after the WatchFaces update to API 30+, users who bought a watchface and, for example, have a ticwatch with Wearos 2.x.X can no longer install the purchased watchface after a reset of the watch. Or is there another solution?
As I understand it this works the same as Galaxy Store. The watch faces are simply not “discoverable” meaning that you can’t search for them and they are not on any public lists. However, they are still in the store.
If you go to play.google.com click on your profile Click on Library and Devices then any watch faces you have purchased will be listed there and can be redownloaded.
FYI In Galaxy Store old purchases are in Receipts in menu at the bottom.
For some reason very few people know about this. 
Ron
Samsung Developer Relations