On Twitter, a webmaster wondered why Google added an additional unnecessary variable at the end of an indexed URL of his website. John Mueller answered that Google does not make up URLs and that the URL probably can be found on the website.
In general, we wouldn't make up URLs like that, so I imagine we found them as links somewhere. With the normal canonicalization methods you can usually encourage our systems to focus on your preferred URLs.— 🍌 John 🍌 (@JohnMu) November 25, 2019
How to check if these errors exist on your website
The website audit tool in SEOprofiler finds unexpected URLs on your website. Many people are not aware about the errors that they have on their web pages. The website audit tool finds these errors and it also shows you how to fix them: