The .138 update is now up on the US Asus support portal (may need to check under Driver & Tools instead of BIOS & Firmware), and likely other regional portals, too (it notes "for TW/WW/EU/RU").
There doesn't seem to be any notable differences from the .133 update, aside from the security patch being updated to June (.133 has the May security patch).
And no, color banding/black crush is not fixed.
Other than that, the usual Android 11 functionality and features.
Strange, I'm on three and vodafone and there is neither VoWIFI or VoLTE for me on either network in the UK.
I just got the official update,
Overall, the animations and all have slightly changed and some ui changes.
The haptics have been improved. It feels abit more stronger than android 10.
But, just one problem is that there have been alot of frame drops while opening the app tray , but no noticable frame drops while opening apps or inside the apps. Only while opening the app tray I noticed significant frame drops (at 144 hz) . This didn't happen on android 10.
The black crush issue is not fixed at all. Like not even one bit.
Please fix the black crush issue in the next update.