Pro tip for your home maintenance fans. If your toilet is filling more slowly or has stopped filling, rather than replacing the filter mechanism right away because your know how to fix this, check to make sure there isn't a small filter (which is clogged) where the water supply connects to the filter mechanism.
Clean or remove that filter first. It's a much drier* operation and takes only minutes and usually no tools.
It won't be drier if you don't shut off the water supply first and there will be a bit of water so have a small pail and towel handy.