I want back up my 7plus

Marking your own post as Solved may prevent others from trying to help because they think you have fixed your problem.

See if anything here helps.

Backups – Choose Method.  -

Back up your iPhone or iPad to your Mac using Catalina or newer OS.

ASC YouTube for how to back up your iPhone, iPad, or iPod touch to your Mac

Back up your iPhone, iPad, and iPod touch.  *

Back up – What does iCloud back up.  *