Universal Android debloater is a pretty safe tool to use if in recommended option. So I don’t think there is a need for a backup. However since UAD uses adb to disable things if your os breaks, you can restore the last disabled packages via fastboot.
For backups, can’t twrp backups be copied via USB? If your phone is famous enough you can find stock images on its site or on XDA developer website.
However, do note that QFIL tool is a very powerful tool and it’s very easy to softbrick the device if you don’t know what you are doing. Find a video for your device to be double sure.