When I click the "ASCOM" Radio button on the "Add New Telescope" window in Stellarium, it activates the lower portion of the window.
I had to click the lower scroll up/down arrows (circled in yellow in the pic below) to find the input to select the type of ASCOM telescope.
When I click the "Choose ASCOM Telescope" button (big red arrow), it pulls up the ASCOM interface where I can choose the POTH Hub (or alternatively connect directly to the PMC 8).
I'm curious if you get these inputs, and if so, can you get it to work for you?
Mounts: EXOS II PMC-Eight, LXD75
Cameras: ZWO ASI294MCPro, ASI385