Hello, Richard
Just to be absolutely clear, I think you're stating you can't drag audio from the timeline into the browser and make a music loop file. Is that correct?
Sorry if you made it clear in the above text, but I honestly don't get your issue fully.
It could help showing a video of the issue if you have a screen recorder etc. If you have a Nvidia GPU there is Geforce experience that I use a lot and could help with, but that only if you have the right GPU.
I'm not a support agent, just a normal user trying to help.