I just discovered that myself! I had everything Google-related that I could find on my phone disabled, which is why I couldn’t figure this out right away. When I enabled Google files, I was able to go to Apps and download the apk by sharing it. However, it won’t install on my wife’s phone, which makes me think that when I switch to GrapheneOS that it may well not work there either. In any event, I won’t have any scruples pirating it since I already paid for it!