Actually it is an OS limitation. Android 10 system initially do not allow enable gesture navigation when user set third party launcher as default launcher. According their announcement, they will gradually open the limitation in future updates, therefore, some devices may not support android 10 gesture with third-party launcher like MSL at the present.
Please find more details in their announcement link https://android-developers.googleblog.com/2019/07/android-q-beta-5-update.html
Attach a screenshot from the above link for your easy understanding, too.
· How to check if Android gestural navigation is supported on your mobile device?
(1) Open system settings on your mobile
(2) Go to System -> Gestures -> System Navigation. (Below illustration is on Google Pixel, settings page may vary across device manufacturers)
(3) Single tap radio button to turn on “Gesture navigation” .
(4) In case you are unable to find the navigation setting page on the device, please refer to the link for further assistance: get help from your device manufacturer