I play on the Steam Deck directly rather than on a TV, which might be part of it. In the past, I've had noticeable input lag with some 4K TVs even when playing a Switch directly docked into it, so it might be worth ruling the TV itself out as a potential source of error (e.g. by seeing if the same input is noticeable from the PC to the Steam Deck directly, or if you use something hooked up to the TV directly).

In terms of the wifi itself, I have two mesh routers in the house, one directly connected to the modem in the living room, and the other upstairs in my office, with the desktop plugged into it via ethernet. I'm lucky enough to be in an area with gigabit fiber, which made it seem worthwhile to invest in a good mesh setup, and I honestly might ended up with fairly low local latency mostly by accident from that. I've read some things that indicate that WiFi 7 might be a significant part of why this works well for me, but having never tried streaming games before having this setup, I don't have anything to compare it to.

On the software side of things, I mostly use the defaults that the AUR `sunshine` package comes preinstalled with for the server (although I'm not sure how much of that is tweaked from upstream). I don't have any ports exposed to the wider internet, and I have LAN encryption disabled, which likely reduces the overhead a bit. I'm not sure if it matters, but for the sake of completeness, but my GPU is a Radeon RX 6900 XT, and I'm running the standard Arch repo versions of of mesa, Plasma 6, and the `linux-zen` kernel (with Plasma configured to use Wayland rather than X11). On the client side, the Steam Deck is using Moonlight from the flatpak listed in the "Discover" app in desktop mode, with the resolution set to 1440p (since that what my monitor has, and I've found a lot of games lower the quality of the graphics if I lower the resolution to match my Steam Deck's native 800p) and the refresh rate set to 90 FPS, which the app then displays as converting to a bitrate of 49 Mbps. I have it set to fullscreen (since I don't really have any need to use the steam deck for other things when gaming, and it still does allow me to easily get back in to the local settings without much issue even with that set) and Vsync off, the boxes checked off for "Optimize game settings for streaming", "Capture system keyboard shortcuts", "Enable mouse control with gamepads...", "Enable HDR", and "Unlock bitrate limit" (the last of which presumably overrides the auto-computed bitrate mentioned above), as well as turning pretty much every audio setting I can off or at least to the lowest possible value since I'm pretty much always either watching TV or listening to music nowadays when playing. I left the video decoder and codecs as "automatic".

The only two things that ever seem to go wrong is that the Steam Deck sometimes seems to decide to render the on-screen keyboard below the streamed desktop rather than above it, and occasionally (maybe once every 10-12 hours of playing over several days?) the connection will start to degrade over the course of a minute or so and become unable to sustain the necessary bandwidth. The keyboard issue seems like it might be a bug in Moonlight, since I'm able to fix it by disconnecting and restarting the client itself, and the connection issue seems like it's either an issue with Sunshine or my network itself, since I can always fix it by simply disconnecting (without needing to restart Moonlight itself). The experience overall has been so good that I've almost completely stopped playing anything locally on the Deck itself (with the only exception being occasional emulation of Gameboy Color/Gameboy Advance games, which obvious don't require much in terms of hardware). I'm able to play games with much higher graphical settings than I could locally on the Deck, and the battery life is significantly improved (maybe around 6-8 hours of dedicated playing). It's such a smooth experience that I've been seriously considering upgrading to the Legion Go literally just to have a higher-res screen for this setup without having to change much (since SteamOS is supported for it nowadays; I don't have much interest in the Legion Go 2 with Windows, and the more powerful/efficient hardware wouldn't do much for me with my current setup).

[1]: I didn't have a ton of experience with mesh wifi honestly, but after some basic research I ended up buying of two of this mode (which seems to have a version of 6.1.0 from checking just now)l, and they seems to work reasonably well: TP-Link Deco BE25 Dual-Band BE5000 WiFi 7 Mesh Wi-Fi Router https://www.amazon.com/dp/B0DKVKLJX3