Itch-io is an unofficial client application for Itch.io which allows you to browse / download free/paid and legal indie games for various emulation systems directly from your device.
Your purchased games (such as from game jams) can be downloaded after entering your personal API key, giving you access to your library.
Releases for muOS can be downloaded by selecting the file with the muxapp extension here: Releases · carroarmato0/NextUI-Itchio-Pak · GitHub
If you have any issues, feel free to create a Github Issue with as much details as possible.