GPU: AMD Radeon RX 5700
Host Device: Windows 10 
AMD Radeon Software: 20.4.2 (2020-04-23)
Client Device: Amazon Fire TV Stick 4K
AMD Link: 3.0.200317; 3.0.200429 (2020-05-01)
UPDATE: The connection problem has been solved with the latest AMD Link version on Fire TV! I can now establish a stream from my computer. Picture and sound are subpar though. Network test tells me, that I've got at least 50 MBit/s bandwidth, so no problem there. But the picture becomes corrupted all the time while playing a game. Parts of the picture freeze or show heavy artifacting. Sound is only stereo and compression should aim for higher quality. In this state it's still virtually unusable.
I've got a problem with the AMD Link app on my Fire TV Stick. The app won't establish a steady connection to my computer. My computer shows up in "Connect to a PC", I click on it and type in the PIN number provided by the Radeon Software on my Windows PC. Connecting to my computer looks fine, at first. It shows me the screen with the message "Connected to MyComputer" in the upper right corner and the search button (magnifying glass) in the upper left corner -- but nothing else (see screenshot as an illustration). The screen lasts for about two seconds, then I'm back to the connection screen.
I've tried AMD Link on my Samsung Galaxy S7 and there it works! I can connect and stream my desktop on my smartphone without a problem.