Audio editing in Final Cut

Where are you sharing from? You can share a clip from the browser, or you can mark a selection in the timeline with in and out points and export that section of the timeline.

For an excellent introduction to FCP start with Steve Martin’s 60 minute intro. For a more in depth introduction use the Izzy video tutorials. The version is a bit dated but the principles are the same.

Learn FCP in Under 60 Minutes - YouTube

Final Cut Pro Tutorial | Izzy Video

You didn't mention which audio editor, but something like X2Pro with FCP can export an AAF file (Advanced Authoring Format) that an audio editor like ProTools can open. An AAF can include "handles," or extra media beyond your edit points allowing for fine tuning and can also maintain FCP Role assignments that get turned into tracks in ProTools. I wish that Logic Pro's integration with FCP was better and have sent Feedback to the dev team.

There's a Hum Remover in FCPX, too. Personally I've had horrible results, often my results are worse than the hum itself. But yeah, Export window lets you decide between audio, video, or both to export.

Gregory's Playlists.

I think it's a personal link for YouTube Studio. Isn't this the wrong link?

I have found that the slideshow themes using Photos are clunky and often have blank frames.

It's best to create slideshows with FCP.

You could use the export function and select Audio only, choosing the format you want.

XML is just a data information file. Use the Share button in the upper right. In Settings in the first pop select Audio. You can choose to export AIF or WAVE. Don’t use MP3.

Have you tried FCP's Voice Isolation?