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As if it wasn't bad enough that they want me to use a random internet service to add a keyboard to a usb wifi receiver, they have the balls to put this for Firefox users. I clicked out of pure curiosity, as I'm not even remotely interested in involving a corporate internet service in getting my keyboard connected to my computer. This is the message you get now on Logi Options software if you have a Unifying Receiver: 
For the curious: https://logiwebconnect.com
EDIT: some people on the thread have brought up that the error message being displayed for Firefox users is due to the WebUSB API not being implemented by Firefox due to security concerns. This still does not justify having to use a web app to plug peripherals to a PC.
you can still do this without the webapp https://wiki.archlinux.org/title/Logitech_Unifying_Receiver
Is that for Linux only or can you use it on other OS's? I don't own this device and probably wouldn't need it, but if I find myself given a nasty surprise like this after buying something I'd like to be able to bypass the bullshit but I'm also unlikely to be using Linux.
Logitech has supported pairing multiple peripherals to one USB receiver for quite a few years now. It's usually part of the driver package