Google seems to use PageSpeed Insights scores so that very slow sites don't appear in the search results very much. In other words, having a horrible score can really hurt your site, but it isn't necessary to get 100/100. If you site score at least an 80/100 I wouldn't expect improving your score to help your rankings further.
In August 2021, Google ...
Yes, site speed has been an SEO signal used by Google since at least 2010.
However, it is a less important signal than page relevance. It's more important for mobile searches, but even so it affects about 1% of searches.