No. You're not required to use the app. You're not even entitled to use the app. If you want to use the app, you have to play by their rules. Plenty of device manufacturers have chosen to only offer iOS apps. No one talked about mandating that apps were available on competing platforms.
If you choose to use something like GrapheneOS, you are signing up for the fact that almost no one will test on your platform and plenty of things will be broken.
If you choose to use something like GrapheneOS, you are signing up for the fact that almost no one will test on your platform and plenty of things will be broken.