I don't know about mountain bikes, but on hybrids and road bikes, toe overlap is relatively normal. Since most turns happen when you are going fast enough to steer by leaning instead of turning the wheel, we just learn to ride in a way where toe overlap doesn't impact us.

For mountain biking, you would be better asking in the mountain biking forum. My guess is that there may be more need for low speed cornering, but I am not sure if a mtb riders tend to address the issue in the same way. However, if you are set on a new crank, to make it easier, seek out a crank that you can use with the existing 113 mm square taper bottom bracket. You will need a crank removal tool, but otherwise, it is a pretty simple change.

The earlier message you didn't understand was refering to the usual method of coasting through the corners to avoid toe overlap issues, but you can't do that if you are riding fixed gear...