You can use PeerTube for audio, and the latest version of PeerTube includes support for podcast feeds that are compatible with podcast apps.
(PeerTube has always had RSS, but the latest update makes it more suitable for podcasts.)
If you upload an audio file to PeerTube, you can optionally add an image too or just leave the screen blank.
Alternatively, there's an audio-specific platform on the Fediverse called @funkwhale, more info about it at https://funkwhale.audio