How much storage does iCloud need to backup?

That depends on your device and the quantity of content on it being backed up. My iCloud backup is approximate 5.5 GB. Some users are far less, or far more.

To see the size of your next backup (and current backup), go to Settings > Apple ID > iCloud > Manage Storage > Backups > {Device Name}. You'll see the last backup time/date, the backup size, and after a few minutes, the size of your next backup.

These directions do not work for 11se2020. Why can't every phone work basically the same way???? Who's job is it to make sure the next phone works different from the one before it? Iphone is more expensive but the texting on an Android is a million times easier.!!!! I have had this phone a year and am still frustrated with texting, and so much more. I have had my first AND LAST iphone.

Yes, they do. Make sure that your phone is up to date (Settings > General > Software Update). But your device, even without updating, should provide the same information.

Texting is wholly unrelated to backup size, but texting is pretty easy, not sure what the frustration is, they all work pretty much the same way.