Just an observation on my part. I have 300 Mbps internet service. My router is approximately 1 ft away from my fire stick 4K. Whenever I use 5 GHz I get much higher speeds. The odd part though is I get much more buffering when using IPTV. I switched to the 2.4 GHz band and no problems, streams perfectly. Might be interference, who knows. I tried all the VPN protocols (Surfshark and IPVanish) and manually inputed dedicated wifi channels on my router.
The point of this post, do not give up on the 2.4 GHz band and default to 5 GHz because of speed. In my case speed is not my friend.