How can I convert a bathtub into a laundry sorting area?

If your tub is up against a wall and does not have a surround, you could attach a hinged board (with hinged front legs) to the studs in the wall. Just lower the board when you want to sort laundry. Put a table cloth/pretty sheet on the board...or contact paper. Use the tub for storage.

If the tub is free standing, just put a table over it.

What ever you choose to do, make sure the level of the folding area is a good one for your height, if too low it can give you an aching back.

You can put pretty bins in the tub. If you can't find bins, build a frame to add laundry bags that you can label such as "whites" "darks" "delicates" or whatever fits your lifestyle. That way you can drop them in or lift them as needed. something like this:

https://decorsteals.com/lights-and-darks-double-bag-laundry-cart.html

Hi ! . Build a frame around it . If that is too much , just measure out the top allowing an inch overhang , if possible . You can even have home depot or Lowe's cut it to size for you ! ( just go at a time they aren't busy ) either way you chose , paint it and place 3 or 4 laundry or regular baskets on top . If you just layed a piece of wood on top , to the overhang area you can attach a skirt by using any fabric and Velcro strips . Or you can have a piece of beadboard cut to size to cover the front . It doesn't have to be beadboard , they have paneling in brick & barnwood

As well . You can use Velcro strips to hold this in place as well. If you do this , lessen the overhang to 1/4-1/2 an inch . Good luck !!!