How to restore from Google 1 full backup?

You can only restore the backup when you start a reseted device, when it asks the Google login and right after the backup option. You cannot restore if you have already skipped this. You have to reset the device again and login and start backup at that first screens. I did this recently.

 

Keep in mind that Google One is just allowing you more online storage capacity, it is not a comprehensive back up service. So you've got more room to store data online, but it's not an backup/restore solution. Also, the backup/restore option buried in the Settings menu is a bit of a misleading misnomer on Google's part -- it refers to Google apps and services so setting and config changes for Google apps and things get auto-backed up but other non-Google data and files are still you're responsibility to archive.
Just how did you backup 'all' your S9 Plus? If you're not able to get Samsung's Smart Switch installed on your Macbook Pro, doing so would require you to root your device to be able to manually copy all those files/data/apps you indicated, and that would also require a rooted device to be able to then manually restore all those same files/data/apps accordingly. Typically some kind of backup/restore app or online service is involved. You could use the Smart Switch app on your phone to back up to another mobile device that also has the Smart Switch app installed but since you indicated you're using your laptop, again what app/service did you use to actually do the backup? Typically you use the same app/process to do backups and a restore when necessary.