The DJI Fly app is probably considerably worse for security/privacy than most Google apps. DJI has a storied history of sketchy practices in their apps: see here.
Google also won't allow DJI to distribute their apps through the Play Store, because of DJI's weird insistence on being able to push arbitrary binaries to customers' phones entirely free of any third party vetting.
GrapheneOS' sandbox hardening might help somewhat, but I'd recommend avoiding DJI products if you can. If you must use DJI Fly, prefer to use it in a different profile where it can't touch any of your personal apps. Tough when they are singularly the best drone manufacturer for videography though.