Is there a way I can backup my Notes on my iPhone 8 Plus

You can either back up your notes or sync your notes to iCloud. These are completely separate processes that do not overlap in function.

To sync your notes go to Settings/[your name]/iCloud and turn on the switch for Notes (and anything else you want to sync). Once turned on note sync is automatic and happens in near real time, so your notes are saved as soon as they are created or edited. You can log in to https://icloud.com and view them. You can also enable sync to a Mac, or to Windows if you install iCloud for Windows (from the Microsoft Store).

If you do NOT sync notes as I have described, they will be included when you back up to iCloud, but they will be part of the phone’s complete backup, and not accessible separately. To get them back you would have to restore the backup, which will overwrite everything on your phone.

Yes, why not? Simply enable iCloud sync for Notes in Settings > Apple ID > iCloud.