This has come up a little bit before: Google indexing same page multiple times: Issue with canonicals
If I’m following this conversation correctly, this seems to be referring to a slightly different issue than what I’m talking about above. It’s not a problem to create multiple canonical URLs for a topic if they’re grouped by 20 replies at a time and have unique meta descriptions (page=2, page=3, etc). The problem is when a new URL is created for every individual reply within a topic (/2, /3, /4, etc).
For a topic with 100 replies, the former would result in 5 URLs per topic (100 replies grouped into multiples of 20). The latter would result in 100 URLs per topic (a new, individual URL for every single reply), which creates a big SEO problem.
how were you able to determine that this was a significant contributor? a lot of SEO posts made here have been fairly speculative, so some evidence goes a long way!
With tools like Google Search Console, SEMrush, and Ahrefs. All of them highlighted warnings and errors resulting from the massive number of URLs on our site that were being created by these forum topic replies, all of which were being indexed by Google without providing substantial new content. Health scores were in the 30s and 40s when our forum was public. Once we locked down our entire forum and made it private (so Google couldn’t see it) and re-ran the tests, our health score went up into the 80s from this change alone.
I have no experience with this plugin and can’t vouch for it personally, but someone has attempted to disable canonical links entirely with a plugin before: Remove Canonical Link Plugin
I found this as well. Unfortunately, this plugin actually makes the situation worse, because it just removes canonical tags completely while still keeping the /2, /3, etc pages, so these additional URLs are still seen as low-quality duplicate content.