The “load whole thread” option is a good idea. For a 10,000 post thread that might be a problem for a browser on a phone. But that doesn’t mean it couldn’t be available for asking and work fine on a real computer. I suspect some of the reason it isn’t directly available is to put an obstacle in front of content scrapers that love to steal messageboard content and repeat it elsewhere on ad farm sites.
See here for a sneaky technique that will load the entire thread that you can then browser text-find through as you and @Guinastasia want: