if you're looking for a dedicated art program with a simple layout i'd recommend firealpaca or medibang paint, speaking as a user of both.
both are free to download, offer tons of free brushes (medibang simply need you to set up a cloud account, also free) and allows you to make your own brushes; not to mention a fair amount of filter, editing and screentone options and other comic making tools. plus firealpaca has an onion skin mode for flip book/frame-by-frame style animation