I don’t think there is a way to forward cellular phone calls. You’d need a phone provider which provides that feature, like a Voice-over-IP provider. Or a SIM card in your computer. Plus the right phone contract.

Kdeconnect can forward a lot of other things though, like SMS, files…

I wish there was a way to hook into calls. But as far as I know they’re deliberately keeping that closed.

There is no direct way to forward calls with KDE Connect or any other app, but there might be a solution if you would mainly receive calls at home.

If you’re willing to learn and configure, you could setup a PBX server with a Pi or an old machine by installing Asterisk and setting up your phone as a trunk line for it via Bluetooth (I’ll find the instructions soon)

The only way I found is using MacOS (even the old versions) for doing this. The sync platform is the only one that don’t cause me any delay or influence the quality of the call. Are those calls from the SIM? If it is whatsapp or other app I think you can answer directly from the client on the computer.

You’re probably not talking about landlines. Some routers can act as voip servers which you can connect to with clients like Twinkle. I use that with my Fritz!box.