Parsec does not pass motion to the host itself, but you can configure the emulator and controller program to take the motion data through the internet. This guide applies to anything that uses the UDP server, so controller programs like DS4Windows and BetterJoy on the guest, and emulators like Yuzu, Ryujinx and Dolphin on the host.
Parsec 150-88 added specifically the Dualsense feature set, which works as long as all connected guests have a Dualsense controller connected via USB. Learn more. For other controller types, the guide below still makes more sense.
To transfer the guest's motion to the host, and not have to deal with port-forwarding stuff, you'll want to set up a VPN tunnel between the guest and host. Expand one of the options you’re interested in below.
The person with the controller needs to tweak the IP used by their own program, in their own machine. Expand the controller program you want to configure.
Now the host should set up the emulator to use the guest's motion. Expand the emulator you want to configure.
Parsec may also end up using the ZeroTier/Tailscale IP for the connection. If you notice people's connection experience with Parsec is worse than usual, you can confirm whether Parsec is using the guest's ZeroTier/Tailscale IP by going to Parsec > Help icon > Console. Whenever someone joins, the IP used shows there in the line that starts with net.