Oh boy… You don’t know what “cloud” means.
If an app stores info on their servers, they have access to it. This isn’t something only big tech does. Any app may store user account information, general app data, etc. if you can use it on your desktop and you can use it on your phone… guess where that data is…. ☁️ 🧠
As I said above, what we need are more apps allowing the use of private data storage. Your own “cloud” (server). And then an OS level block of all network connections besides that single source.