Q.cabbage
Why are leaves turning pale green?

This is most likely a nitrogen deficiency issue.
You can use Blood Meal for a quick dose of Nitrogen.
Read and distribute according to the package directions.
You may also want to have a soil test done on the garden soil.
Here are some links to help you.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/blood-meal-fertilizer.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/nitrogen-plant-fertilizer.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/understanding-nitrogen-requirements-for-plants.htm
https://www.gardeningknowhow.com/special/organic/the-importance-of-soil-for-an-organic-garden.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm