Update from this post: https://www.reddit.com/r/biggreenegg/s/Nncx2ojmNv
So I followed the advice you guys gave and 3 weekends of diluted white vinegar and many potato scrubs with salt later the plate looks like this now:
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All rust is almost gone. The harder spots are the corners or the outside of the plate. At this rate it will be ready for summer though.
Last step will be the seasoning and will probably use avocado oil.
by JNachow