A factory unlocked Google Pixel 4a (a Pixel 4a purchased from the old Republic is factory unlocked) is broadly compatible with WiFi calling across carrier networks. Frankly; I can’t think of a reason it shouldn’t work with Boost Infinite other than somehow, they simply haven’t turned WiFi calling on for your account.
I expect WiFi calling on your Pixel 4a will work with MobileX as it does with my Pixel 6a.
Have you seen my reply to you in another topic regarding account credits and refunds?
This is not the topic to discuss the difference between account credits and refunds, so, if you wish, please follow-up about that in the other topic.