I have been doing solar imaging for a number of years. The Newton ring issue is real and a pain, and is unpredictable with many theories re: its genesis, etc. I have purchased 5-6 video imaging cameras, and whether they are expensive or cheap it doesn't seem to matter.
I have a TeleVue Pronto for full disc imaging and I have never had Newton's rings with ANY of the cameras.
However, my TV 102 has it with EVERY camera I have tried.
These rings are a nuisance in and of themselves just by the virtue of being there. I hate seeing them visually, and yes you can process them gone, but it is less than aesthetically appealing.
My answer has been solved with the T2 tilter for my ASI 120mm. It works like a charm, and at ~ $38 USA is well worth it for me.
Thus changing the imaging angle against the plane of the telescope lens has fixed the issue. And yes, I am smiling much for that.
Thank you ZWO [this is not a paid ad] for offering this product.