Yes, it should be possible to just publish an update and have the Testflight app pick up the updated JS bundle OTA. There are some exceptions to that such as if you have upgraded the Expo SDK version or made certain other changes in
app.json. More info here - https://docs.expo.io/versions/latest/workflow/publishing/#some-native-configuration-cant-be-updated-by.
If you built the app with a specific release channel you will need to publish to the same release channel for it to be picked up. If you didn’t specify the release channel for the build or publish then the default release channel will be used for both and it should be fine.
The flow that Expo goes through to decide which published bundle to pick up is here - https://docs.expo.io/versions/latest/distribution/advanced-release-channels/#what-version-of-the-app-will-my.
If you display your version number in your app (from
app.json) then that can help confirm whether the changes are being picked up.
Let me know if any of that helps.