Lenovo Tab4 10 Plus (TB-X704F) reached its end of official software support well before 2021. According to the Lenovo Android Upgrade Matrix
Lenovo cited two primary reasons:
Users can still check for any remaining minor stability patches by navigating to Settings > System > System Update . The Custom ROM Breakthrough (2021) Lenovo Tab4 10 Plus (Lenovo TB-X704V) lenovo tbx704f android update 2021
If you need a newer version of Android (9.0+) for specific features or security: Custom ROMs (Advanced) Lenovo Tab4 10 Plus (TB-X704F) reached its end