If your wiki has been marked as "for kids", they cannot. If it is not marked as such, then they should be able to by default. If the wiki is not marked as "for kids" but they still aren't able to edit without an account, check to make sure that you (or another admin) didn't accidentally disable anonymous editing. To do so, go to Special:AdminDashboard on your wiki and look for the "Wiki Features" module on the right of the page. There should be an option labeled "Require all contributors to log in". Make sure it is disabled. If you do not see that option there, then the wiki has likely been marked as "for kids". If this is the case, you can contact Fandom and ask them to consider changing the wiki's status. If they approve, they will unmark the wiki as "for kids" and the option should be available at that time. Note that it is currently the weekend so you might not get a reply until Tuesday or Wednesday.