I'll also soon recheck the prices of listed VPN providers and also update this thread with Black Friday deals. I think that Mullvad and IVPN won't offer discounts but many Non-Privacy Focused Mainstream VPNs will offer good Black Friday deals.
I checked Proton VPN and Nord VPN and it seems like they do have a Black Friday deal. You can get a 1-year plan for 40 euros for Proton VPN[1], while you can get a 24-month plan for $122 at Nord VPN[2]. I feel like Nord's discount is pretty similar to their 2 year-package deal which happens quite often though, so not sure if this is a nice offer or not. I'm interested in buying Proton VPN but I still have a month of Mullvad, not sure if I'd switch just because of the discount.
[1]
https://protonvpn.com/blackfriday[2]
https://nordvpn.com/black-friday/