First of all - try to touch backplate. 3090 may throttle due to high memory temperature. If its ok - try to add core clock several times per 100MH one time.
I have checked HWInfo and no thermal throttling, only power throttle!
In MSI Afterburner its not even displaying the mV, why would that be do you think?
Also the fan for the backplate that comes with the unit doesnt fit into my case because of another cable

Thanks for replies

You will not see memory throttle, that`s why try to touch. I can`t say anything about MSI Afterburner - i just don`t remember it. Try HiveOS or RaveOS. It`s simple and helps to configure your GPUs easily.