Since I use MyPhoneExplorer for syncing stuff to and from Android anyway, I also use it to copy the whole Internal Storage to the computer, because it can do that and because it can do that via WiFi, which is a lot faster than via USB.
Else I would simply connect the phone via USB to the computer when Android is running, enable data transfer, and copy everything to the computer a file manager (e.g. Explorer on a Windows computer) presents as “Internal Storage” on the phone (which requires MTP to work correctly on the computer side).
If the bootloader of the phone is unlocked already before any current backup attempt, it could also be done when TWRP is booted. TWRP enables MTP once it gets access to the data partition (i.e. once the user supplied the correct unlocking PIN/password/pattern equivalent for TWRP to decrypt the data partition), so Internal Storage can be copied via USB then, too.