The Speedtest app on my A1842 Apple TV 4K shows that the device has no problem with much higher Wi-Fi bandwidth, matching what my current plan is with my ISP (80 Mbps).
Apple specifies a hardware maximum of 866 Mbps for 802.11ac (Wi-Fi 5) in Apple TV 4K. Apple TV Wi-Fi specification details - Apple Support
- Separate from that may be at what speed video can be processed by Apple TV. About the same as iPad Pro 2017, as that has the same chip. It seems that I do not currently have any test files with more that 35 Mbps. 😔
- Separate from that may be at what speed video can be send to Apple TV. For Home Sharing, this part depends on the sending computer/NAS and your home network – not your internet plan, and not Apple TV.
If this is about using a specific app (e.g. Plex), then please mention that, as it might be relevant.
… and all have latest firmware.
Apple TV 4K, tvOS 12
No they don’t. The current system software version for Apple TV is tvOS 15.4, not 12.x.
About Apple TV 4K and Apple TV HD software updates - Apple Support
Update your Apple TV - Apple Support
Routers/Wi-fi access point capabilities (including speed) are mostly set in hardware. So what are its specs? 802.11ax (Wi-Fi 6), 802.11ac (Wi-Fi 5), 802.11n (Wi-Fi 4), 802.11a, 802.11b/g. And do you force 2.4 GHz or 5 GHz band? (It is recommended to let devices choose for themselves.)