Here are my personal thoughts about your dilemma.
As already been said these 2 cars are targeting different needs. The Ioniq 5 is a family car, very good for long journeys with wife and kids.
The MG4 is smaller and despite that it doesn't lacks of room, traveling with kids & luggage's could be more challenging with it.
MG4 is new and as every new car/model has some bugs at his early days. Nevertheless the manufacturer is resolving the issues, because they of course want to continue increasing the sales.
Even long time established manufacturers have issues with new models. Look at the id3 and the software problems they had when it arrived to market.
Regarding the Ioniq 5, I already drove a Hyundai EV for close to 90k km (about 55,9k miles) without any issue and I know they are reliable.
I hesitated in the past about Ioniq 5, but as its suspension is too soft for me, I finally didn't took it.
When I tested the MG4, I was surprised by the way it drives and the fun that we can have with it on the road.
This is only my personal opinion of course: even without taking into account the price difference, my choice would definitely go to MG4 and if there is still any early time issue, I know that the warranty is there for that and my dealer will provide me the needed support to solve it.