I should have thought of [3]/4 - thanks fratveno! There have been several time signature threads - basically, square brackets are a way to override or specify default rhythmic groupings, without changing the appearance of the time signature. [2+2+3]/8 will appear as 7/8, etc.
[3]/4 treats the entire bar “in one”, which can useful for pieces like Beethoven’s Egmont overture, in this thread -