It's in the announcement for Plasma 6.1, see https://kde.org/announcements/plasma/6/6.1.0/
To enable it, you need to use the Brightness & Colour widget. See also the merge request for this: https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/4093
I guess the documentation is a bit lagging still! I don't know about a list of compatible keyboards, but I suppose you can just try it out to see if it works! 😁
There's a protest coming up for this too (as well as to remember those killed and injured):
On Tuesday, October 22 join the active transportation community to remember those people using active transportation who have been killed or badly injured on Ottawa's roads in the past several weeks, and to protest Queen's Park's anti-cyclist proposed bike lane law. Meet on the north side of City Hall at 110 Laurier Avenue West at 5 pm for a rally and then protest ride.