The voice notes used by YakBak and now Nostur are a different note kind than would show up in most Nostr clients' default feeds. Those clients would need to add support for that note kind.

That said, there is nothing stopping you from just recording your voice as an MP3, uploading it somewhere, and pasting the URL into a regular kind 1 note. Some Nostr clients will display it as playable within the app while others will just display the link, though.