Can someone help me with canonical url issue please

I have a forum website that has been doing nicely for a few years. I hadn't bothered with Google Search Console for a while but decided to set it up again as I wanted to see what the clicks were as was thinking of setting up adsense advertising.

So I set up Google Search console and all looked well. But I have now messed things up and not sure how to fix it. In the inspect url section I kept putting in links from forum threads and it was coming up with this is a duplicate and something...

Can someone help me with canonical url issue please WordPress ...