If the M3U8 file contains a line like #EXT-X-KEY:METHOD=AES-128,URI="key.bin" , the tool handles it automatically. But if the key is injected via JavaScript, save the key as a .bin file and paste the absolute path into the "Decryption Key Path" field.
Because the GUI relies on the N_m3u8DL-RE engine, it inherits powerful technical capabilities: nm3u8dlre+gui