Gary Illyes from from the Google Search Relations team posted another PSA on LinkedIn, this one says "don't use relative paths in your rel-canonical." Gary wants you to use the full, absolute URL, when it coms to rel-canonical.
Here is his post:
This is not new advice, Google said this in 2018 and in 2013 - but that is why this is a PSA from Google.
So much so, John Mueller from Google also shared what Gary wrote on Twitter:
Canonicals and relative URLs, what's up with that? Find out more at https://t.co/gJenmsuFv6 from your friendly neighborhood house elf.
— John Mueller is watching out for Google+ 🐀 (@JohnMu) January 30, 2023
John explained why, is the why is not obvious to you, John said, "One of the problems is that it's relative to where the content was found. www or non-www? http or https? staging subdomain? staging domain? random other domain that's hosted by the same company? If you want to pick something specific, it's good to be specific."
Forum discussion at on LinkedIn.