I really liked this informal community poll and thematic analysis on SLO usage. It does a better job at highlighting the hurdles to adopting them at a Company Who Is Not Google than a lot of "Here's how to do SLOs" things just don't cover.
If there is ever a "Seeking SLOs" book, this should be the first chapter.
https://ericmustin.substack.com/p/notes-on-service-level-objectives
