How do you boost a post? Went back to my old post and I'm not seeing the option on my end.

You boost a post like you upvote it. After your first upvote, all your subsequent upvotes are considered boost.

Note: that boost decays pretty fast with time since the original submission. The older the post the more upvotes (and yet even more boost) a post requires to rank higher.

I might change this in the future. Rather than using the time since the original submission I might use the average time of the upvotes and boost rather than the time of the submission.

I was trying to boost this FAQ in hopes that it would show up in the "Front page" (and thus in the /rss fee), so that new posts would automatically occur in the @StackerNewsFeed account on Twitter and also on Mastodon.

Is there a (reasonable) amount of sats that would cause this to happen (for this post from back in July)? Or does the rank algo just make that infeasible?

Ranking algorithm makes it infeasible.

Adding a math plugin to my markdown editor is on my todo list ... so I can show rather than tell what the ranking algo is among other things.