control - How to find Phase crossover frequency?

I make the imaginary part of \$loop \ gain=0\$ to find phase crossover frequency.

But in one video, the person told that this method can only be applied when Polar plot crosses the real axis and cannot be used when it touches the real axis.

I don't get why he should be right as Imaginary part equated to zero implies the phase is either 0 or pie or point lies in origin then where does touching and crossing came into the difference.

Also, will I consider such point that is if polar plot touches real axis as \${Kmarginal}\$ for calculation of \$Gain \ Margin\$ using formula \$\frac{Kmarginal}{Kgiven}\$?