I have added a picture showimg the problem of old addons staying inside the world settings. As you can see in this example there are 3 versions of "Expansive Biomes" in this screenshot. In total there are 5 versions on this world setting, however I couldn't fit all of those into one screenshot
Thank you for linking me to the other ticket, OcelotOnesie. Weird that I didn't find it, because I did try to search for active issues on the matter before opening this one.