This is an interesting question because it all depends on what you mean by ‘backed up’. In one sense, yes they are backed up as they are all stored on a Google server, so if you completely wipe your phone for example you’ll still be able to access your Google Keep notes. But, if you were to permanently delete all your Google Keep notes and then completely wipe your phone, then there’s no way to recover those notes.
Personally I regularly create copies of my important Google Keep notes on Google Docs (which is a nice feature that’s built right into Google Keep). That way I am backing up those notes in a separate area so should something happen to my Google Keep account, I can still access the notes that are important to me.
Alternatively, you could choose to regularly download your Google Keep information from takeout.google.com which is another great way to backup and store data that you don’t want to lose.
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