Flourished at first but now the leaves are turning neon and the stems are shriveling from the end to the soil.
Growing Mint Indoors
Certified GKH Gardening Expert
It looks like your plants are in a container too large for them. A small container of soil is best for such small plants. Too-large containers are prone to holding onto too much water, which can damage the plants' roots- this may be the cause of your problem.
Try gently digging up each plant with its roots, and repotting the plants in a small container with good drainage. In the new container, check the soil moisture at the surface and water when the surface is dry.