The problem for Lineker is that it WAS a penalty. I've watched it again on YouTube, slowed right down. Harry tries to back heel the ball (fails) and immediately Cash slides right into his standing leg, from behind, up-ending him. Watch it from 1:48 on 25% speed, if you don't believe me.
All Harry is guilty of is jumping to minimise the impact (understandable, given his ankle problems) and over-playing the pain - but they all do that these days.
I hate to say this, but Mike Dean and VAR got it right.
Edit: ...If Sanchez had done the same to one of their players we could have had no complaints about a penalty.