I backup to both .csv and unencrypted .json. The .csv file is easier to read because you can load it into a spreadsheet. The .json file is better for importing into Bitwarden. You can use any text editor to look at it, but it is not all that easy to read. I encrypt both files and store them in a secure location.
There is also another way to backup which I just learned about from @grb which you can find out about here: