Yes, you can absolutely download and install custom brushes for Krita. In fact, its robust support for community-made resources is one of the software's strongest features for digital artists.
The Krita community is highly active, and you can find high-quality brush packs on several platforms: Where can I find and search krita brushes for download?
Custom brushes are typically shared as ( .bundle files) or individual presets ( .kpp files). Here is everything you need to know about finding and installing them. Where to Find Custom Brushes