Welcome to the Forums @irene-zaz1.
As you mentioned the Mate 20 is currently not part of the supported devices list. That is not to say that it will definitely not work but the app has not been fully optimized to work with that phone. As long as it fulfills the minimum requirements, Android 4.4 and Bluetooth 4.0, there is a possibility that it can work but we cannot guarantee it.
If you do try to sync and it doesn't work, some users of unsupported devices have mentioned that following these steps helps with the syncing. It is certainly worth a try.
Alternatively you can sync with a computer or another mobile device and use the app on the Mate 20 to check your stats and your data and not necessarily sync with it.
Feel free to reach out with any further questions.
Lanuza | Community Moderator Remember to vote for posts that helped you out! Tired of the same workout music? Try a Podcast! 🙂
Community Moderators ensure that conversations are friendly, factual, and on-topic. We're here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
Best Answer