According to geomantic theory, old porcelain cups and bowls can't be thrown away casually, right?

You should be talking about archaeology! Where did you hear or see such feng shui? Ceramics are quickly updated and easily damaged. If they are damaged from the perspective of geomantic omen, they must be replaced immediately, so that there will be no feeling of ruin and decay. As for what you said, don't throw it away casually. I think it's more reasonable to understand that success won't catch people. Don't use it in feng shui.