Ok, is the battery, charging 0 issues saving the Game finally, i try 3 times on charging and all good, i gonna try with battery nowNothing like that in my SP and it does have the colour of someone spilled something or dirt from your bag got in the slot. Could also be causing what you see so I would consider getting it out of there.
Worse is it looks like it is on the GB/GBC slide as well (the little slider just to the right is what detects when a GB/GBC cart has been put in and sets things accordingly, others reading along if your screen boots up in GBC mode then check that is not stuck down).
As it is on on the pins (we hope anyway) you can probably mechanically do something there. I would get a wooden or plastic tooth pick (stuzzicadenti?) and see if I can remove a bit with one of those, though I have steady hands and have done this a lot so if you are not that then get someone that is as bending one of those pins would not be good. Fortunately if it is food then they usually respond to IPA and other such solvents far more readily than most things making pins dirty.