Mobvoi Ticwatch E3 (mobvoi-ricefish)
Users owning this device
ADB and Fastboot Over USB
While a bluetooth connection can be used for ADB debugging while booted into Android, a wired connection is necessary for doing anything in Fastboot. Unlike some Wear OS smartwatches, the TicWatch E3 has a 4-pin connection on the back, which can be used for a USB connection. However, the included charging cable only has 2 pins, which do not carry data.
Some people have found that the old charger from the TicWatch Pro 4G (which had 4 pins and allowed data transfer) can be modified to fit the TicWatch Pro 3. The TicWatch Pro 3 and E3 should be similar enough that this method will still work. See this Reddit comment from someone that got it to work.
TODO: try modding a USB cable for this and report back.