Disclaimer: This is a community workaround (not official). Please advance at your own risk.
Since about 30th June, people using the Paris datacentre have been experiencing really high latency but only while using Virtual Desktop or the VR app and not while using the desktop or mobile app.
If this is what you experience, try this simple fix!
If you just get a high ping in general, this will likely have no effect.
Step 1: On your Shadow, Open Settings (shortcut: win+x, n) then click "Network & Internet"
Step 2: Click “Change adapter options”
Step 3: Right click "Ethernet" and click "Properties"
Step 4: Click "Configure…"
Step 5: Find “Large Send Offload V2 (IPv4)” and change “Value” to “Disabled”
The stream will break, so quit Shadow (Win+Alt+Q) and reconnect.
Quit the Virtual Desktop Streamer app and re-open.
Enjoy VR streaming without the insane latency!
If this doesn’t work, try disabling “Large Send Offload V2 (IPv6) too.
Many thanks to @Jamielamb#0279 on the Shadow Discord #vr-chat for figuring this out!