SeekingGoodTech
Hey, I am in the same boat. Work laptop with Iris Xe that is not usable whatever I try. With the difference that they do not care and would not do anything to propose an alternative.
For the dithering - it might not be the thing that is bothering you. If you have an access to a personal laptop with that card, try it.
What I can offer is the following - try with eGPU. If you have a GPU that you are sure you do not have any issues with, it is possible to "attach it" to your working laptop and let it do all of the rendering fully bypassing any video cards the laptop has. For this to happen, you need your laptop to have thunderbolt ports. Also, you need IT to allow you to use PCIExpress (in a corporate environment this is generally forbidden for obvious reasons - you can essentially connect any external hardware to your motherboard). But since they actually understand you have issues and are willing to cooperate, they might give you an exemption. Also, you'll need to install drivers for your external video card but this isn't a shady unlicensed software so it shouldn't be a problem either.
Before going to the eGPU route, make sure you have full authorization from IT. For example, I did it without asking IT and realized it is forbidden but I have already spent a bunch of money on an eGPU enclosure. Also, keep in mind setting this up is tricky and will require efforts. Having an eGPU isn't so streamlined and OSes need some tweaking - you'll have issues with bitlocker and other stuff. Once you set it up though it's not a big issue.