Aluminum wiring with dark discolouration on outside
Yeah, it looks like slow-cooked wires

The type of damage you have appears like the cable jackets have slow-cooked themselves from extended overheating due to overload.  While properly terminated aluminum wiring is normally OK to keep around, the overheating damage means that the cause of the overheat/overload should be found/corrected, and the damaged cabling runs replaced outright.