The ash and the gas sulphur dioxide (SO2) emitted by volcanic eruptions are a major hazard to aircraft.
The two planets are very similar, but a detailed comparison shows the differences.
The very high surface temperature of 474 °C hardly varies from the sunlit side to the night side.
The planet Venus used to have lots of water, that has been completely evaporated. CO2 remains in the atmosphere of Venus.
Venus' atmospheric composition in percentages show 96,5% of CO2 and less than 3,5% of N2.
Venus’ atmosphere has a thick cloud layer that covers the planet, extending from 30 to 90km.