1)
You consider this about the Linkedin site but don't stop to think about other social networks. This is true about basically all of them. You may not post on Facebook, Bluesky, etc, but other people may like your links and post them there.
I recently ran into this as it turns out the Facebook entries in https://github.com/ai-robots-txt/ai.robots.txt also block the crawler FB uses for link previews.
2)
From your first post,
> But what about being closer to the top of the Google search results - you might ask? One, search engines crawling websites directly is only one variable in getting a higher search engine ranking. References from other websites will also factor into that.
Kinda .... it's technically true that you can rank in Google if you block them in robots.txt but it's going to take a lot more work. Also your listing will look worse (last time I saw this there was no site description, but that was a few years back). If you care about Google SEO traffic you maybe want to let them on your site.