This was mentioned in #1009 already.
Defaulting this launcher switches to 2-button/3-button navigation from gesture navigation mode.
Quoting you, from this thread, for reference: https://www.xda-developers.com/latest-action-launcher-beta-adds-support-android-10-gesture-navigation/
I'm personally not convinced that there is any point in trying to support something that is likely to disappear next Android update -- Google really doesn't have a good track record of maintaining its own idea, but they're very good at forcing developers to update their apps to follow their crazy ideas, without even offering basic support of documentation.
Anyway! If anyone is interested in looking into this, feel free :) But I'd recommend waiting for official APIs to be released (or for the feature to die, axed by Google)
If they are planning to kill the gestures in the next major version, this feature is not worth enough to be worked on.
Not saying it will, but Google has been testing new ways to interact for the past 4 years and so far, none sticked around for more than a couple versions.
Closing for now, can reopen if future versions of Android make the new gesture more usable.