Seeking recommends on storage solution

If you don't need any features like automatic syncing between devices: A big ass hard drive what you put stuff on.

If you do: Probably Proton Drive.

I run something called Nextcloud. It is a 'personal cloud' type server with easy app integration for automatic backups. You can run it on a computer at home, or you can run it on a commercial VPS. You can connect as many clients to it as you want, and choose which ones get a copy of what data from the others.

If this sounds like something you might be interested in, I highly recommend you take a look at a project called Yunohost. It is a nice and easy way to get started with hosting your own services. Once it's up and running, you just install apps (ie, Nextcloud) and it takes care of the configuration for you.

The proton thing is fine.

Proton is absolutely 100% undeniably a honeypot but if you’re not doing organizing or big boy crimes on it you’ll be fine.

E: the reason I don’t say a drive plugged into your phone is that as of a few years ago it was unclear in the moment what was manually backing up to an attached drive. This may have changed recently.

I personally roll with a Synology NAS for local storage. Synology is wicked user friendly.

Proton has a decent storage solution

Buy an external hard drive.