I’d say, not totally impossible. But on Earth the first multicellular life arose only half a billion years ago. So it took over 4 billion years to get to complex life like us from the first life on Earth.

The thing is we just don’t know if that is typical. Venus could easily have had microbial life in the past if Earth is an example.And it’s possible that that life still exists in its clouds.

The idea here is that Venus started off Earth like in the early solar system. But at some point it dried up, lost its ocean due to a runaway greenhouse effect, which didn't affect Earth in the same way because continental drift on Earth continually buries and circulates the carbonates.

Though the surface of Venus is amazingly inhospitable, the layer at the top of its clouds is in many cases the most habitable location in our solar system after Earth - almost Earth like in temperature, pressure, and atmospheric composition (without the oxygen of course). It has one major drawback, droplets of concentrated sulfuric acid.

However we do have acidophiles on Earth that survive in conditions not far off the acidity of Venus clouds - in sulfuric acid outflows from mines on Earth.

So - it's possible that there is sulfuric acid tolerant life in the Venus clouds. The other main problem with the high Venus clouds is that there are no solid surfaces of course. But it could have evolved in the early solar system and then migrated to the clouds as the surface got drier and hotter.

The main question is, could the life find some way to stay aloft? The residence time of particles is months rather than days - so - that makes it easier, and turbulence could return some of the life to the tops of the habitable layer after it reproduces - but it's still quite a challenge.

So, we might find out about ancient Venusian life from its descendants if they still live in the clouds. If not, there’s another way we could find out. At present with its thick atmosphere it’s almost impossible for meteorites to get from Venus to Earth even with a ten kilometer impact. So far at least, we have no Venus meteorites.

But in the early solar system, the Venus atmosphere may have been thinner, and the impactors were larger too, of the order of 100 km diameter upwards.We might have meteorites from early Venus elsewhere in the solar system.

If so, the easiest place to look for them is on the Moon. It would be rather astonishing if they developed a civilization there so quickly when it took so long on Earth. But we might find evidence of meteorites from the early solar system on tge Moon, from at least the end of the “late heavy bombardment” in the form of meteorites on the Moon and incorporated into the regolith and it may have meteorites from early Mars and Venus. Back to the Moon: The Scientific Rationale for Resuming Lunar Surface Exploration, section 3.1.1