Also though, playing devil's advocate here, maybe City haven't breeched the rules? (I am pretty sure they have, but bear with me)
Maybe their global income is good enough to sustain the spend, whereas Forest (and Everton) did exactly what FFP is meant to stop - sudden huge splashes of cash on the hope it generates enough profit (success) in the short term to make them compliant? Man City have been spending big for years (and receiving huge income too), whereas the 'sleeping giants' of Forest and Everton simply cannot sustain it.
Don't slate me, just trying to throw out an alternative.
FWIW, I do think Man City have unfairly spent and used their financial backing to buy success at the detriment of the other teams.
Think the City charges go back a decade so while they're income now is likely huge it certainly wouldn't have been back then.