4k video
jacab
obs, flameshot/sharex, and 7-zip
also, the sponsorblock addon works on mobile and there is an addon that allows videos to play in the background if you need that. i haven't tested this with youtube music in the browser but i wouldn't be surprised if it also worked.
pipepipe and rimusic is what i use. youtube in the browser is fine too, if you disable that "open in the youtube app" popup (firefox for android with ublock origin addon is what i use, although i have experienced some regressions with the ad-blocker not working after youtube updates something, but ublock is usually on top of it and fixes stuff quickly).
also syncthing, if you'd like to synchronize a directory to act like a shared folder and be identical on both devices
KDE Connect
nixcon north america was sponsored by anduril https://nixos-users-against-mic-sponsorship.github.io/
I think NixOS would stand to benefit a lot by taking inspiration from openSUSE's YaST system configuration tool. I think that if NixOS had a well supported graphical interface for creating and managing the system config, it would become so much more accessible to a very wide range of users who never would have given it a try otherwise, which in turn would bring in tons of new users and developers who will want to improve nixpkgs, etc.
you can install emudeck on any regular linux distro
with dolphin specifically, you don't want to connect the wiimote through the bluetooth interface, as dolphin has it built in to handle wiimotes already; see https://dolphin-emu.org/docs/guides/configuring-controllers/#Real_Wii_Remote
It would be great if Plasma gets a kiosk mode option some day, that seems right up KDE's alley as far as the "simple by default, powerful when needed" philosophy goes.