I will verify. seeding should not cause this might be Windivert drivers as app itself doens't look into those packets.

Can you try with 4.0.2 beta version.

4.0.2 beta : consumes 3-5% of cpu without any rules , passive start

3-5% is of course less, but it is still more than consumed by qBitTorrent, which works with the disk, encrypts data, and operates multiple connections, while ProxyBridge does essentially nothing.

You should check doc. ProxyBridge run 2 different relay server. Accepting and parsing and processing packet is fully cpu task. Does nothing is not what ProxyBridge does :) normal encrpytion takes less cpu compare to a server that open port and accept packets and handles and tested with 100k packets. Each task perfom multi cpu operation.

You are welcome to open a pull request to update the tcp and udp server code with no cpu impact :)

Also you mentioned its more than torrent app it self. App sending packet is managed by network stack of OS. It doens't impact any cpu. ProxyBridge run tcp and udp server that will have a cpu. Comparing both is invalid.