What are some of your favorite book series that seem never ending?

I've been documenting a lot of books I read as a kid on my book tracking app. A lot of them are series that seem(ed) never ending: baby sitters club, Nancy drew, Hardy Boys, magic tree house, etc. They're also all primarily stand alone books, there isn't a need to read all of them.

I'm curious if anyone has recommendations for similar series. I don't mind what age range they're intended for, I'd just like to get more chill reads. I usually don't re-read stuff as well, otherwise I'd just re-read all of these lol.