restore iPhone from backup

[zio_mangrovia]

I'm going to reinstall iOS on iPhone 11 so I locally backuped It both to MacBook and to iCloud.
My target is to reinstall iOS because sometimes I have issues on calls.
I have doubts about these procedures:
restore by backup which I run on MacBook Pro
restore by iCloud, resetting device to factory default.
I'd like to understand what exactly make these procedures.
Procedure 1 reinstall iOS or copy alla data which are on Mac to iPhone ? That is, if device has X free space before restore It will got the same free space after restore. What happens ?
Procedure 2 reinstall iOS ? It uses recovery image of iOS ? Can I got major space if app were reinstall again ?

Thanks