When I opened my survival world (created in 1.16 initially) in 1.17 for the first time, I went mining for netherite, but after approximately 2 hours I couldn't find any. In my other worlds, I could find plenty, so I used an Xray and it turned out that there was no netherite in my survival world. Not at all. (I should have saved my world before opening it in a new version :/)

So I think that this bug only affects worlds switched from 1.16 to 1.17, since the worlds I create in 1.17 have netherite in them.

Thanks for your support.