Can't draw as fill with the paint brush

I'm using An2021 and I don't have the option to "draw as fill" with the paintbrush tool which I see in the documentation; at the moment I can only constantly go to modify>shape>convert lines to fills which isn't viable.
My PC meets the requirements, everything is up-to-date and Animate should be running on the GPU; I've had success before on a different pc with An2020 though or at least the same effect.