Yes you can refrigerate cooked spinach.
Cooked spinach keeps better in the refrigerator than raw spinach does.
Although you can refrigerate both raw spinach and cooked spinach and they will both keep just fine.
To refrigerate cooked spinach just make sure the cooked spinach has cooled down first and then put the cooked spinach into a sealed airtight container.
Or put the cooked spinach in a food bag that you can remove the air from.
Cooked Spinach will last for up to 5 days in the refrigerator before it goes bad.
After 5 days the cooked spinach will spoil and should be thrown out.
You can also freeze cooked spinach and the frozen cooked spinach will last for up to 6 months.
To make cooked spinach taste better you can pour some vinegar on the cooked spinach which makes it taste really good.