Can you tell us what wiki it is, for starters?

Thuis wiki

nergensbeterdanthuis.fandom.com

Right?

The font looks fine for me on that wiki and it did when I firs saw this thread. So unless they are talking about a specific page, I don't think so.

For example, this page: https://nergensbeterdanthuis.fandom.com/nl/wiki/Seizoen_26_Week_1

It looks like this:

The page looks fine to me:

What device and browser are you using? Is it possible you, someone else, or some program changed your browser's default font weight?

Thank you for your replies! I found out that the problem occured because I installed Helvetica Neue on my Windows 10. Appearently it's a common error, found the fix after some Googling. Thank you, fixed!