This answer quotes Marc Rayman's August 21, 2018 Dawn Journal entry:
Not all solar system bodies need such protection. The Moon, Mercury and Venus, for example, have not been of interest for searches for life or for prebiotic chemistry. For that reason, spacecraft are allowed to land or crash on those worlds because there is no expectation of subsequent biological exploration. Also exempt from such rules are tiny asteroids, including two that are being explored this year, Ryugu and Bennu. They are entirely unlike giant Ceres. They are often mistakenly thought of as being similar because of the oversimplified notion that all are asteroids. We will provide an illustration of the dramatic difference in the next Dawn Journal.
This might suggest that Venus might not require planetary protection because it has not recently drawn astrobiological interest.
On the surface there is no doubt, but the possibility of life in the clouds of Venus has gained some traction (see here, for example). Would considerations of Venus' atmosphere have an impact on future planetary protection needs for Venus? Considering historical missions, is it already too late for that?
And what exploration or theoretical efforts are underway to assess any possibility of cloud-based life at Venus?