I also thought about the the rear wheels being tucked in issue, honestly I will be probably going with rims that make the car wider. ET is what we look for here in Germany to determine how much the wheel is going to be pushed outside.
I believe a small change can make a big difference when it comes to looks so I won't be going down the route of spacers. I'm happy with a few mm per side. I've tried spacers in the past and I immediately noticed a change in the car's behavior and I didn't like it.
Also the largest rim I'm ready to put on the car is 18", I feel like 19" is too much rim and too little rubber and would compromise handling and comfort too much.
Currently I really like the Autec Uteca in 18" with ET of 38 which I think is fine.
Alternatively there's the MAK DaVinci in 18" which looks like the Uteca but with slim spokes, which is available from MG in Denmark but not in Germany, weirdly enough.
Else the CMS C28 with ET37 seems like a good option as well.
But I would really fancy the CMS C32 Aero in 18". Currently they're only available in 19". There's also a 18" but that's not compatible with the MG4 in Germany, at least for now. They would be quite a hassle to run legally, you have to get them approved on your car and that can always fail because of the employee that looks over it and the whole procedure will also cost about 100-150€. So there's the risk of buying the rims, mounting them on the car, meaning I cannot send them back, driving to the authorities and if I fail I have to sell them with tyres on the used market with a significant loss.
I still have 7 months to wait for the car so there's no rush, but it's good to know that there are alternatives on the market already.