Cryptomator on Graphene OS

Months ago I bought a lifetime license for Android and now I am ready to set up the app. I have a Pixel with Graphene OS and I don’t want to use Google Play. Which is the right solution for me? If I have understood correctly what is written in the set up guide, the apk and the Accrescent seem to be the more flexible in term of use for my situation. Am I right?

Other questions:

for downloading APK is required to pay for a licence, but as I have already payed for it, can I just download the APK, install it and then put the licence code in the app once it is installed?

Which are the differences in using APK or Accrescent?

Thanks