I feel so incredibly silly right now.
Here’s what happened: I found a guide (Secure your project | Kirby CMS) on securing my project and followed its instructions to add .htaccess files to the specified folders. Removing these files now works as expected.
However, I didn’t realize that the starter kit already included the correct .htaccess file in the root directory. Even though I usually read documentation, some parts can be overwhelming when I’m dealing with something new.
It’s probably a good idea to keep this topic on the forum in case others make the same mistake. Thanks for the heads-up!