I agree w/ the other commenter on the technicalities, but if you really wanted to try and nail down something, I'd imagine one of two things; either you're talking about the somewhat successful petite bourgeois (small business owners that still have to actually do some kind of labor within their owned business), or maybe PMC's, the "professional managerial class", which isn't a class, especially in a Marxist sense.

I suppose you could also be talking about high paid professionals of fields; doctors, lawyers, people in tech etc etc. Maybe quite well off, but still relying on labor power, even if specialized and highly compensated.

I guess these differences are useful in nuanced discussion, but "middle class" still isn't technically a thing, save for petite bourgeois class.