i purchased my unlocked note8 from hong kong last year. after extensive research, i came across shortcut master to modify IMS settings to enable VoLTE/video calling and i was happy. this has been working fine with Android 7.
i have been reluctant updating to andorid 8 since its release back in May due to issues (mainly battery) reported by other users. i recently updated to android 8 in order not to fall behind now that android 9 is the latest OS. needless to say, shortcut master no longer works and i was not able to enbale VoLTE/video calling.
this has been very frustrating to say the least. i refuse to flash the rom to root the phone just to enble features that should have been there for all phones (locked or unlocked).
we bought the oneplus standalone (not from the carrier) and VoLTE works just fine. my next phone will not be another unlocked samsung phone if they refuse to resolve this for their customers.
It's pretty well known that the unlocked version of the Note 8 doesn't offer carrier specific features such as Video Calling. There are workarounds (as it seems you have done previous to the upgrade), but with every trick/work around you cannot expect it to remain the same after an upgrade as said feature was never supposed to be there from the start. If there are people having problems on the carrier version, it's a different problem unrelated to yours. It's on Samsung + carrier to fix the carrier phone, but it's on nobody to fix a feature that was never never supposed to be there.
Now, I understand your frustration. I bought my mom and i unlocked Note 8's from best buy (we are on verizon). I don't care for the carrier specific features but my mom does so after all her whining I just flashed her phone with the stock verizon rom which will not trip Samsung knox nor does it root it. Its just like you have the carrier version, if you for someone reason want to go back to the unlocked rom you can flash the stock samsung rom BUT even sticking with the tmobile rom the phone still stays sim unlocked.
Now for me, the no bloatware outweighs the loss of wifi calling/video calling but each person is different.
So I guess the first step is to figure out why you picked the unlocked version to see if flashing the stock rom is an option for you.
PS: xda forums would have better responses than here as a good portion of users here aren't power users so they only know (from a customization standpoint)what they've already read online (probably from xda or android central)
Since this feature wasn't available from the unlocked models were introduced to the market, it isn't an issue to begin with. nothing to solve or even talk about. if u can find a way to make this happen with 3rd party app or creating ur own code, then good for u. but once again, it is designed not to have the feature.