Is it bad for SEO if the same page is available from multiple urls?

Question

Search Engine Optimization

домен/katalog/kategoriya-1/kategoriya-1-2
Hello, tell me please, there are categories of goods, the default
домен/katalog/qweqweqweqweqweqe/kategoriya-1-2
url of some category is this: not right ? When the site is indexed, pages will be duplicated, right?

Thank you in advance for your response.

Answer 1

You need to read about the canonical attribute.

Answer 2

Counter question: why are you doing this?
Those. I suspect that you want to redirect the user instead of 404 errors to the most relevant page?
If everything is as I asked, then duplicate pages will appear in the search results and the site will begin to lose positions.