Linkedin job posts have a free tier which means a posting can be left up indefinitely whether the search is active or not. Indeed posts cost a minimum $5/day, so a given company would likely take the listing down if their search is not active. I've heard that Linkedin is actively resume harvesting, for what reason I don't really know (maybe training some resume AI?) so it could just be a rumor, but I have a chip on my shoulder about Linkedin anyways for trying to make a pay-to-win job search platform.
Whatever you do, don't apply at the individual job board. Go to the company's careers page to see if its even still posted and apply there. For whatever that's worth (not much in my experience).
I was referred to one by a friend personally, she gave me the name of the person that helped her find a job when she was unemployed. Apparently if your resume is shiny enough they will come to you via linkedin. Other than that there's looking up firms or individual recruiters on google or linkedin that have good relationships in your desired industry/locale, giving them your resume, and hoping for the best.