Is this a losing square?
Python 3, 112 50 46 42 bytes

-4 bytes thanks to Jonathan Allan!

-2 bytes thanks to xnor!



lambda r,c:abs(r-c)*(3+5**.5)//2==max(r,c)


Try it online!

Based on the formula for cold positions in Wythoff's game and making some modifications in order to produce an explicit formula. Explanation inbound once I actually finish a proper methodology for the derivation of the formula.