

I have both strong opinions on things and suggestions.
The Windows software stack is completely independent of the Linux software stack. This doesn’t tell you anything about the problem. Trying Windows tells you that the hardware has the capability, but you could have learned that from a spec sheet.
If you want to solve the problem on Linux, make a post with the details of the problem and what you’ve tried so far as well as any logging that you can get out of Sunshine which would show you starting Sunshine and starting a stream.
Without any other information:I read the fantastic manual.
It looks like you’re likely running into a documented problem: Mesa has disabled VA-API for legal reasons
Without vaapi support, sunshine falls to software encoding which means the encoding is running on your CPU and that is what is causing the stuttering, so to fix it you would need to install a version of mesa that’s been compiled with the correct flags (h264enc, 265enc).
The instructions for doing this depends on our distro. On Arch, amdonly-gaming-mesa-git is listed as an optional package for the AUR version of sunshine, amdonly-gaming-mesa-git is compiled with video-codes=all which will enabled the h264, h265 support.

Those do not enable forwarding. One prints the value of forwarding and the other loads the config file.
To set it temporarily
To set it permanantly, edit /etc/sysctl.conf (or add a config file to /etc/sysctl.d/). You only need to add one line that reads ‘net.ipv4.ip_forward=1’