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)
> Be an uncultured swine
> Visit a European country with rich culture and history
> Summarize your visit by trying to make fun of the grammar of the local language.