Kage no Eiyuu no Nichijou-tan - Vol. 1 Ch. 5

[MisterPinkie]

Welp, I gave it a try and boy howdy is it exactly the same as at least 3 other ex-military mage goes to magic school to live a normal life (but can't) I've read. It's not quite as samey as those strongest mage gets mage racism-ed and decides to reincarnate 1000 years later but magic sucks now because a demon cult tricked everyone to do magic badly so now he's the strongest-er (also exact same mage racism still exists), but it's very close.

 

[ShinduPK4]

This is like a garbage version of "The Irregular at Magic High School", but with the MC being a moron who can't decide whether to hide his ability or to show it off.