When it comes to privacy and security, I think you should treat all cloud providers equally. Use a client with client-side encryption so that the only thing that touches the provider is encrypted data.
Rclone is an example of a good client that can do this, and can even mount your cloud storage as a filesystem with its encryption layer in between.
Good luck!
If you can’t get a packaged apk directly from the developer/publisher, or from a trusted repository like the play store or fdroid, I wouldn’t resort to third party sources like these. If you can’t compare the signing signature of an apk from an untrusted source to that from a trusted source, you can’t be certain that what you’re installing hasn’t been tampered with.
https://grapheneos.org/faq#device-lifetime
You can buy a used Pixel 8 and it will be supported by Graphene through 2030 at the very earliest, probably the best support lifecycle you can possibly get on a phone.