Lunatask looks incredible! Almost too good to be true …
Before I switch from Joplin, I wanted to do some research.
The app itself, privacy etc looks great. But there are some things that will probably stop me from switching 
As privacyfounder mentioned:
It also doesn’t seem to work on GOS with Exploit protection compatibility mode.
Not possible to download APK alone (source). It’s not a dealbreaker, but to install another store just for one app …
If you use a degoogled Android distribution, search for Lunatask on the Aurora Store. Distribution via an APK is not possible.
But what is kind a dealbreaker for me is not be able to use the app completely offline. Of course I want synchronization, but with Joplin I don’t need to log in anywhere to access my data. And to cite their website:
[…] then you will probably wake up one day logged out of your account and your data will be gone.
That’s not really something I want to experience.
EDIT: Another thing that grinds my gears. FFS, let me see/try the app without any registration! 