It is possible, I have my own personal cloud that is in my cupboard. That's where all my files live and I can access them securely from anywhere, and my calendar is on there. It also hosts a minecraft server and streams video and music to all my devices.
You can even host your own email server but I don't do that. It's easier to use something like Protonmail if you want privacy.
But to host your own cloud you'll need to learn about servers, relevant operating systems, cloud hosting software and security certificates and port forwarding and all kinds of exciting stuff.
I think, unless you were particularly interested in that stuff, you probably wouldn't bother.
Unfortunately, the tech industry has decided that the cloud is the way forward and they're going to push everyone to use it as much as possible.
Currently it's mainly files but increasingly processing will be done on remote servers, applications will be 'served', not running on your own computer. The goal, if you talk to big tech, is 'Everything as a Service' (EaaS).
You can resist for a while but eventually you'll be forced to comply!
_________________
The Andaman Sea, the Andaman Sea, I'd like to be, on the Andaman Sea.