Is there software available for free to check Concrete sites for broken links? or what software is preferred?
You could do a google search or…
Try: https://error404.atomseo.com/
Or: https://www.drlinkcheck.com/
Or: Free Broken Link Checker - Dead Link Checking Tool by Ahrefs
a good powerfull old tool (client software, not accessible as a SAAS), compatible windows-mac-linux: LinkChecker - Check websites for broken links