Put this code in your Asus phone dialer app:
*#*#3642623344#*#*
And now go to Settings / Network & Internet / Call / Wi-Fi calling.
After reboot the phone repeat this process.
Enjoy!

From Zenfone 9 (16x256)@Android 13 > 33.0804.2060.100
Retired: Oneplus 9 Pro (12x256) | Huawei Mate 10 (4x64) | Lumia 650 (1x16) | Lumia 1020 (2x32) | HTC Mozart (0,5x8) | SonyEricsson Satio (0,25x0,13) | SonyEricsson K850i | SonyEricsson Z300 | HTC Touch | Nokia 8850 | Nokia 8210 | Trium MT 040 | OneTouch Easy Amena | Motorola Amena M3688 | Motorola Micro TAC