Before putting in my order for a shim, I actually bought some of the copper shims from amazon for my 3080. These specifically: https://www.amazon.com/gp/product/B08JLFR67Y/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Soon as I saw them I knew I wouldn't be putting them on my GPU. Quality 100% inconsistent after measuring with calipers, not to mention they weren't designed for this particular application. There's youtube videos of people sanding them down and getting them within spec but it's a lot of tedious work, and my time is worth a little more than that. Even if you do all the work, if you don't get the results you are expecting you then have to 2nd guess all your work on each shim.

for a $2000 GPU -- you want something that was created with absolute precision.