This is the explanation from the Nova guys.
PLEASE READ THIS IN FULL
Everything mentioned below is still present with the release of Android 11 on September 8th, 2020. Google has made it very clear that they have no plans to completely fix gesture-related issues any time in the near or even distant feature.
Please take note that Google admits to this being broken on their end of things and that a fix will be coming in a future update to Android (stated March 2019).
However, it's now well over a year later and there are still many issues with full system gestures and 3rd party launchers on both Android 10 and Android 11. These issues will remain for the foreseeable future as Google have now made it clear that they have no plans to completely fix their full system gestures.
Notable issues with gestures on third party launchers include:
• Close all/Clear app button not appearing(scroll all the way to verify it's not there)
• Not being able to tap icons for a short time after returning to the home screen
• Animations not being as fluid as expected
Please understand, there is absolutely NOTHING WE CAN DO TO FIX OR CHANGE THIS IN ANY WAY! Contact Google or your device OEM directly with these issues as we have absolutely no control over it whatsoever.
Samsung Users
Samsung has allowed full system gestures to be used within 3rd party launchers with their One UI 2.5 update. This means you can now enable and use gestures, but there are still several issues regarding animations and the like.
As stated, there is nothing that Nova (or indeed any other 3rd party launcher) can do about this and it is ultimately up to Google and OEMs to fix navigation gestures.
Google's statement and Nova's statement
Google:
https://android-developers.googleblog.com/2019/07/android-q-beta-5-update.html
Nova:
https://help.teslacoilapps.com/faq/gesture-navigation