Never used naval jelly on a motherboard but have on some psu and case parts to remove rust. I guess if you do as he said and vinegar first then the naval jelly for "a few hours" <his words> it would be ok.
For reference:
"[Loctite] A registered trademark for a commercial rust remover. Naval Jelly contains Water (65-70%), Phosphoric acid (25-30%) and Sulfuric acid (1-3%) in a gel matrix composed of a thixotropic polysaccharide (1-3%), isopropanol (1-3%), Surfactant (1-3%) and Silica (0.1-1%).Oct 17, 2022"

Rust-Oleum: "Date Printed: 8/8/2023,
Chemical Name CAS-No. Weight % (less than)
Phosphoric Acid 7664-38-2 30.0
D-Gluconic acid 526-95-4 5.0 "

Both use near 30% Phosphoric Acid. one has sulphuric acid other has D-Gluconic acid....me thinks they work the same.

You can buy phosphoric acid at Home Hardware where it's sold as "Safety Acid" for descaling things.

edit: if you've got a decade old bottle of CLR, that might have phosphoric in, but they took it out of sort of "general use consumer products" because the phosphates were contributing to algae blooms when treated water released. Occasionally the Dollar Tree gets in a batch of that sort of thing that still has phosphoric in, gotta read labels.

Any way, you need to rinse it off well with water afterwards or over a week plus it will keep munching at the metal.