I've run the android TV version on a Sony x85 TV, Pixel 3A phone, Tivo Stream 4K, and Chromecast with Google TV. It can run fine on all of them but maybe should not be. You need to make sure the drive is formatted as internal strorage(it will erase everything on the drive and format it). Then go into the server user interface to select the correct folder on the external drive for storage.
If you are using more than one client to view content the TV as server will slow down do to lack of processing power. I'd suggest a hardwired laptop with an internal harddrive if you can afford it to eliminate possible issues. If you are set on using the android platform, I had best results with the Tivo Stream 4K with USB-C Dongle with external hard drive and ethernet. Channels DVR is the only app consistently running on it.