I have two ZZ plants that have stems and leaves that are half-way breaking the soil. The leaves on the stems are medium to dark gr
een, but the leaves in the soil are yellow at the bottom and only light green at the tips. Is this a sign of root rot?
Allow the soil to become dry at the top to the touch between watering and do not over water. It's best to water this plant less than too much because over-watering can cause stem and rhizome rot.
It appears the plant is too deeply planted into the pot. Leaves should be above the soil surface. You can repot and place it correctly in the pot. Make the pot has an adequate drainage hole to allow excess water to drain.