To me managers can have fanboys in the media/online for different reasons but being over rated is when it's shoved down your throat.
Internationally Southgate for getting the players to get on for instance great job. Tactics and anything else on the pitch questionable at least but he gets a free pass and lorded so definitely over rated.
For the Prem its probably anyone linked with top jobs like De Zerbi ok they can be great but it's not consistent so why would it translate to Liverpool or whoever challenging for 4 trophies a season.
So even though I think he has done a good job that is over hyping.
The other way those that don't get enough credit I would go for Rob Edwards. Pound for Pound punching above his weight competitive in each game. They will probably go down but he deserves a lot of credit.