@SyborgCrow
English is a funny language:
... using Opera off wifi ...
meaning
... using Opera on wifi ...
i.e. no mobile data!
It should just work.
I have a spare Android phone with no SIM.
Maybe there is an Android setting to give Wifi priority over cellular?
Opera AI says it should work by default:
If a Wi-Fi network has no internet access, Android will automatically switch to cellular data if "Mobile data" is enabled, regardless of Wi-Fi strength.
Connectivity stability is often improved by disabling "Adaptive Connectivity," a feature on some devices that manages network switching to optimize battery life but may occasionally interfere with network selection.