Dave asked: “I use the app called “Keep.” What can I do to prevent from losing the data that Keep has kept?”
Dave, the information you “kept” in Keep is backed up by default.
Keep is a Google product. You may be using it on a computer or a phone, but much like Gmail, Google Drive, Google Sheets, and every other Google service it’s really web-based.
Anything you add to your Keep is synced to Google’s servers, so if anything were to happen to whatever device you’re using Keep on, you can log-in on a replacement device and find all your data there, or you can even just use a browser and go to keep.google.com from any device.
Needless to say, Google doesn’t see a reason to let you backup your data easily, but you can back it up, just not from within the app.
If you want to download your notes as an HTML file, you can go to takeout.google.com, select Keep and download an archive of your data.
You probably won’t need it, Google obviously backs up, but if you want the added peace of mind, that should get you what you need.