Updated: after doing the research I should have done before posting that Marked couldn't handle this, I simply had the HEAD requests that were getting 403-405 errors fall back to GET requests. Now I get green for all of them:

This will be out in the next update.
Previously, on Marked Support:
Those first two are actually 404s:
curl -I https://support.google.com/programmable-search/answer/13315956
HTTP/2 404
I don't know how Google's server is redirecting, but the URL is returning an error code. Marked can't do what a full web browser would do when redirecting a URL, it can only read the headers, which in this case say the link is missing.
That last one, though, returns a 200 on the command line, but I think that the server is denying Marked access because it's not recognized as a browser. Again, not much Marked can do to circumvent this if the website owner doesn't want anything but browser traffic.