Yes, you can manually select which cellular network to use on your Apple Watch:
Manually Select Cellular Network on Apple Watch
1. Open the Settings app on your Apple Watch.
2. Tap Cellular or Mobile Data.
3. Tap Network Selection.
4. Turn off Automatic to enable manual network selection.
5. Your Apple Watch will scan for available networks. Tap the network you want to use.
6. If prompted, enter the network password using the watch keyboard or Scribble.
7. Tap Join to connect to the selected network.
Your Apple Watch will now use the cellular network you manually chose, even if your paired iPhone is connected to a different network[1][3].
To switch back to automatic network selection:
1. Open the Cellular or Mobile Data settings on your Apple Watch.
2. Tap Network Selection.
3. Turn on Automatic.
Your Apple Watch will then automatically use the same cellular network as your paired iPhone[1].
Note that manual network selection is only available on Apple Watch models with cellular connectivity. GPS-only models cannot use cellular networks[1][3].
Citations:[1] https://support.apple.com/en-gb/119601
[2] https://support.apple.com/en-us/111818
[3] https://support.apple.com/guide/watch/connect-to-wi-fi-apdff5efc8fb/watchos
[4] https://discussions.apple.com/thread/254358319
[5] https://discussions.apple.com/thread/253181817
[6] https://support.apple.com/en-us/102359
[7] https://discussions.apple.com/thread/250250159
[8] https://support.apple.com/fr-fr/119601