Tried to place condenser on Nauvis and got this error:

Error while running event quality-condenser::on_built_entity (ID 6)
LuaSurface API call when LuaSurface was invalid.
stack traceback:
[C]: in function 'index'
__quality-condenser/scripts/combinators.lua:21: in function 'create_for_struct'
quality-condenser/control.lua:289: in function <quality-condenser/control.lua:212>

I have only two surfaces: Nauvis and one space platform.

that error seems to suggest that you've manually deleted the surface called "quality-condenser", and unsurprisingly that broke the mod of that name.

to fix it just remove the mod, save, and then re-add the mod.