comments:
paulmarchant posted on r/electronicsrepair2w
It's rust. Rust is not (despite what people here seem to think) soluble in Isopropyl (or any other) alcohol. The cat piss... that's water based, and you'll do a much better job of cleaning it off using hot distilled / deionised water and then drying the board thoroughly. As for the rust... it's not doing you any harm, and the most sensible thing would be to leave it alone. If you're desperate to remove it, then one of these: https://www.amazon.com/TAURISH-Fiberglass-Electronic-Applications-Corrosion/dp/B0DT9P7C62 is your best, near-zero risk approach.