https://www.amazon.ca/Amazon-Ethernet-Adapter-Fire-Devices/dp/B01LXP5TXI/ref=sr_1_1?crid=3FN4D6TBMR86G&keywords=fire+stick+ethernet+adapter&qid=1646797111&sprefix=fire+stick+eth%2Caps%2C95&sr=8-1

you get one of these with a FireCube, but I bought them for my FireSticks. they sadly are 10/100 not gigabit, but I have yet to find any media or streaming that didn't work. I have used Plex and Kodi on the 4k FireSticks with HDR and Atmos connecting to my local NAS and never had any buffering or frame dropped. NetFlix and Amazon Prime also have zero issues with the connector. I have seen some 3rd party adapters that say they are faster, but I went with the OEM as that way if there is any issue, it's Amazon who needs to figure it out.