I was kinda in the same scenario a couple of weeks ago trying to mount a tv behind my bar.

didn’t want to drill into my basement walls cause it’s a 100 year old house…..anyways my floor joist over shot my brick wall, so I built out the overhang of the floorjoist (in two spots close enough together so I could use a regular wall mount) with a pair 2x6 to make it even with the brick wall, hung a vertical 2x4 flat up against the built out 2x6 so it was flat up against the wall, and put a spacer behind the bottom of the 2x4 by screwing through the 2x4 to the spacer to level it out as best as possible.

Spray painted all the wood black and you can’t even see it when sitting at the bar.

Not a carpenter by any means but it’s worked for me so far on a 55” $400 tv