There is a very similar thread to yours that I posted below and copied to yours.
No regrets at all. I purchased 2 months ago a Blue M3/16GB/512SSD.
I still have a 2018 MM i7/32GB/512SSD on a 38” Dell 4K in the basement office. It still a worthy computer minus the super weak GPU. I have a external eGPU I can hook up to it if I need to. I will keep it till it is no longer usable for what ever reason.
Prior to the MM was a 2015 27” iMac with the dreaded Fusion Drive, that is why I sold it after 3 years of use.
What I really like about the M3 iMac is the obvious beautiful screen, but the sound system to me is spectacular, the mic and video for teams meetings is top notch. The gaming on this thing is excellent. I finished Resident evil Village and now in the middle of Resident Evil 4 remake. The few cables I have compared to the MM makes for a very clean desk. I have one plug going to the outlet. It’s the fastest computer I have owned.
I would/did consider a New Mac Studio Max over a MM because of the 32GB Ram standard and more ports, faster computer.
The basic 4K screens out there are good but they don’t compare to the 4.5 iMac., or a 5K.
If I did team up with Mac Studio then it would need paired with Studio display, that would be one sweet setup but $3,600 + roughly compared to $1,900 for my setup. Studio to Studio Means great internal speakers and mic/video, less clutter.
The negatives I found with the MM probably true for Mac Studio is everything does not always work with non apple accessories/devices. Or did work until the next software update. I know, I lived it
Regardless these are all personal preferences, and all 3 of those computers are really good computers.