Is Google Drive a backup?
The short answer
Not really. Google Drive is a sync service that mirrors your working folder. Deletions, overwrites and ransomware damage reach the cloud copy too. Its version history typically keeps 30 days and 100 versions per file. For full protection, pair Drive with a true backup service.
In detail
Google Drive does its own job well. Your files follow you across devices and sharing is easy. The free 15 GB is generous too. Just keep in mind that "my files are in the cloud" and "my files are backed up" are two different promises.
It helps to walk through a few situations. You delete a folder and empty the trash. After 30 days it is gone on every device. A file gets corrupted and the corrupted version syncs. Older versions are kept for 30 days and 100 revisions. Restoring hundreds of files one version at a time takes a long while. If ransomware encrypts your synced folder, Drive uploads the encrypted files as designed. And if your Google account gets locked or hacked, you lose access to everything at once. Version history cannot help with that.
If your life runs on Google, keep using Drive and Google Photos for daily convenience. Then add one layer underneath. The easiest is a true backup of your computer that includes your local Drive folder. Backblaze and IDrive can do this. At the very least, set a calendar reminder for a Google Takeout export. Keep a second copy of your photos and documents at another provider as well. An encrypted one like Sync.com or Proton Drive is ideal.