Hi, and welcome to the forum.
While I don't know the specifics of PopOS, it does very much seem to a problem with the audio routing in the OS, rather than the device.
Are you developing an app to use the device, or is this a general operations issue?
I would suggest you try something like the following (I can't tell you whether this is applicable, though, as I don't have any experience with PopOS).
If you still can't make it work, it could be a product issue. If you have the possibility to try out on a Windows machine (eg. borrow one), you can check if the device works.
For product specific support, you can go to jabra.com/support and raise a ticket.