Recover media from Android backup files
TWRP allows backup for devices with no external MicroSD Card. Therefore TWRP does always exclude Internal Storage from backup. They recommend manually copy Internal Storage via USB-MTP (which makes sense after creating  TWRP backup because it contains TWRP Backup folder too). If you know how to unpack/repack recovery.img you can add this fix (experimental) https://forum.xda-developers.com/showthread.php?t=3941108 this will allow you backup of Internal Storage from TWRP