In addition to that, Wi-Fi Calling has not yet been listed under Maxis’ name on Apple’s website. That being said, several Lowyat.NET Forum members said that they were able to obtain the feature on their iPhones.
The availability of VoWiFi for Maxis customers is definitely a long time coming given that its competitors such as U Mobile who had rolled out the feature way back in 2016 which was then followed by Digi in 2017. Now that Maxis is finally on board, this left Celcom as the only major telco that has yet to provide VoWiFi capability to its users. (Thanks for the tips, @hiw200 @SLeong123!)