Venusian lower atmosphere qualifies as a supercritical fluid, but there isn't any clear liquid-gas interface (a surface layer) where Venusian ocean and its atmosphere would come in contact with each other. Actually, this dense lower atmosphere that reaches supercriticality due to pressure and temperature only make this boundary layer less clearly defined.
So it's up to your definition of an ocean if you still want to call the lower atmosphere of Venus like that, but I haven't noticed it called an ocean in any planetary science literature, unless they discussed Venusian geologic evolution and potential that it could have once had large bodies of water. And the lack of clearly definable surface, in my view, qualifies as a good reason not to.
Note that even if you still want to call it an ocean, this lack of clearly defined boundary layer also means that you'd have problems establishing its volume.