There are mountains and deep canyons on the bottom of the ocean here on Earth, so it seems that pressure doesn’t matter much. It’s all light as air compared to the pressure underground with the overburden of rock!

The temperature does affect things, as does the gravity and the composition of the air. Much stronger surface gravity will prevent mountains from getting so tall, as under pressure the crust actually flows. Increased heat as on Venus causes rock to flow more readily, so again mountains will be shorter and less rugged.

Lack of water, as on the moon, makes rock stronger, so mountains can be spikier and taller. Other materials in the atmosphere, that gets cycled through the crust, may have effects in either direction.

Now mountains brow due to tectonics. That's not happening on Venus. Is it happening — and at what rate — on your world? Faster techtonic processes will mean more uplift, more rifts, and also more volcanic mountains.

So, it depends on a lot more about your planet than just the atmospnere.

There are mountains and deep canyons on the bottom of the ocean here on Earth, so it seems that pressure doesn’t matter much. It’s all light as air compared to the pressure underground with the overburden of rock!

The temperature does affect things, as does the gravity and the composition of the air. Much stronger surface gravity will prevent mountains from getting so tall, as under pressure the crust actually flows. Increased heat as on Venus causes rock to flow more readily, so again mountains will be shorter and less rugged.

Lack of water, as on the moon, makes rock stronger, so mountains can be spikier and taller. Other materials in the atmosphere, that gets cycled through the crust, may have effects in either direction.

Now mountains grow due to tectonics. That’s not happening on Venus. Is it happening — and at what rate — on your world? Faster tectonic processes will mean more uplift, more rifts, and also more volcanic mountains.

So, it depends on a lot more about your planet than just the atmospnere.