He's always been a good commentator and pundit because he reads the game well and analyses it fairly. Never noticed him showing "bias" during a commentary, but then unlike some football fans I'm not sitting there furiously looking for it. Like them all, he lets people know who his club are and has a joke about it, but it doesn't affect his analysis.
I bet there's a Man United forum somewhere where they are all accusing him of being "biased" because he was very negative about them last night after the game. Correctly.
Mostly this stuff is silly fan talk born from confirmation bias.
He is two faced example bringing up Tactical fouling last season when all teams do it and in games saying thats another tactical foul on our games but when another team do it not a peep! They set the narrative.