Used this guide to backup my pi sd card to a usb drive.
[URL unfurl="true"]https://pimylifeup.com/backup-raspberry-pi/#backing-up-your-raspberry-pi-sd-card-on-linux[/URL]
Followed the last section, just before conclusion.
With cron schedule, the script backs up my sd card as an .img file to a connected usb drive, every day.
Using incremental backup, so just one .img file, no history.
The img file should be usable in balena etcher, rufus, win32 disk imager or the raspberrypi image tool too.
I have yet to test the image generated by the script.
Tbh it should have been done after the first image itself. Hopefully I get some time to test it before I have an actual need for back up 
