We have a few specialized brush bundles and the ultimate pixel art tool ever which is a paid plugin, but if you are really deep in pixel art, then these will be the best spend five bucks of your career as an artist. For brush making look at the end of my post.
At first the plugin for Krita →
and now the bundles →
If you want to create brushes yourself for pixel art, then use the Grid brush engine for your first experiments. To get the best information available for creating brushes using Krita there is this tutorial series, and you won’t find anything more comprehensible than this currently. →
Hello @Tailor, and welcome to the forum!