How to center a large symbol on the origin in KiCad
I don't think there is a way to do what you want with the current feature set. (I am not even aware that something like this is currently planned for a future release but i might have missed something. Head over to gitlab and check if it is at least requested)

You might even consider changing strategy to be honest. If the symbol is so large that it gets hard to see if it is centered then i guess it might benefit from being split into multiple smaller units. A typical split is to separate per GPIO section and separate units for power supply, crystal connections, programming interface, ....
That will allow your schematic to be made easier to read.