I installed 3.5.0 on my 2nd Gen Fire TV Cube and, with a VPN connected (I tried both ExpressVPN and Surfshark) then the app would not work, I was merely presented with a blue spinning circle. Having said that, I don’t know how I’d have even logged in to the Rabbithole app on the Cube as I used my Google account to buy Rabbithole.
I have successfully installed it on my 2019
Nvidia Shield TV and it works OK with Surfshark. The PQ of the EPL highlights looks SD to me but for £4.40 for 6 months I’m not complaining.