Before Digitakt OS 1.21A there wasn’t an easy way to do a backup. You can try ELK Herd, which is a third party tool.
You can also upgrade your digitakt to 1.21A first and use the new transfer 1.4 to backup your digitakt projects before going to 1.30. (Tip: save your projects in each revision of the os, and also make a backup of the projects in each revision of the os).