There is currently no way to use pro audio equipment such as mics with XLR connectivity with GTW. These devices connect to computers via USB audio interfaces like the ones listed below.
In a webinar, it may be desirable to have more than one speaker in the same room, going through the same computer. A USB audio interface can make this possible.
In my experience, these connections sometimes work, but are unstable and, according to tech support, are not supported by the platform.
Suggested ones to start with:
Focusrite Scarlett series
Universal Audio series
Note: Zoom, Google Meet, and WebEx all seem to work fine with these devices.