I have Chinese edition Mix Fold 4 with HyperOS.

I have been able to activate my Google Fi sim (unlimited) in my S24 Ultra and then transferring it to my Mix Fold 4.
Which gave me texting, calling and LTE data without downloading Google Fi app.

I have enabled VoNR and VoLTE, which seem to work.
I have managed to enable "Calls over WLAN" without Google Fi app and using dial codes to enable.
But it does not work.

When I make a call, it keeps saying "connect to WLAN" even though I'm already connected to WLAN.
I tried enabling "Mobile Radio Power" in network, but no luck either.

Mix Fold 4 info:

• bootloader is not unlocked.
• OS version: 1.0.11.0UNVCNXM
• has original build.prop

Was wondering if anyone been able to enable WIFI calling or texting without Google Fi app on HyperOS?

I found this, but don't know if it's still relevant today.
https://xdaforums.com/t/activate-project-fi-account-from-an-unsupported-device-successfully-accomplished.3784430/
Looks like you try to trick Google Fi into thinking your device is supported by updating the Build.prop file with "supported device" information.

Was thinking about using either of these to edit build.prop file in HyperOS.
APP: "Root Browser" or Systemless

Any words of advice? Thanks