Yes, it’s compatible.

He is sure? Because the Viper V3 Pro 8K Dongle does not work with the new Deathadder V3 Hyperspeed.

Viper V3 Pro is a different story (still dunno wtf happened here).

Yes, it’s compatible and the Hyperpolling dongle website confirms it: https://www.razer.com/eu-en/gaming-mice-accessories/razer-hyperpolling-wireless-dongle

But in the Synapse app it is not separated as an independent item, it is linked to the Deathadder V3 Pro.

Strange… the dongle part number is: RC30-04410 ?

Are you on the latest firmware for the dongle? https://rzr.to/V0zxjI

I clicked on this link and even with the dongle connected nothing happens. It doesn't leave the home screen.

Wireless Dongle Model: HSD01

Could you take the photo of the dongle itself showing full P/N?

I think it’s the same dongle as bought separately. But dunno why it doesn’t appear in Synapse (maybe Synapse bug)? You could try the new Synapse (beta): https://www.razer.com/synapse-new

I'll test it in the new Synapse.