There are some sites such as communities and job boards that don’t have any available feeds to source job opportunities from.
This could be because of the nature of the the target site e.g. Dev.to is touted to be “A constructive and inclusive social network for software developers". Its not a job posting site.
Neither is Product Hunt but you’ll no doubt know of the high regards its droves of users have of it, as well as the companies and startups that advertise opportunities on it at $299 for a 30 day run.
Thankfully there's a couple of RSS feed generators to get around this. I’ve used both PolitePol and FetchRSS which have free plans (and time limited feed updates). With either you can spin up an RSS feed from practically any web page.
Sign up for the free plan on either site, and cut and paste the URL of a webpage you want an RSS from. Then pick the page items you want to include in the feed, and you'll be given a URL. Add it to Feedbin using the ‘Add’ feature in the bottom left pane of the reader. Whenever a new opportunity is posted on the webpage, it will update in your feedreader.
Check out these RSS generators at PolitePol and FetchRSS to see if you want to include them in your feed strategy.