I was mostly assuming based on my own experience, as a human. Humans love gathering around large fires. As you asked let’s dive into it.

Here is a bit list of festivals in Germany. This will be my starting place for most of it.

Easter - already discussed too much.

Biikebrennen (mostly a regional thing.)

If one includes fireworks… Well, check out the list of festivals above and word search. There are many.

The Tollwood Winterfestival has fire acts (in the photos at the bottom of the page). While these are very small fires, they look pretty cool.

At this point I asked an AI and it listed three additional. Yes it is shameful that I got impatient. Feel free to stop reading. I did my own reason from the names and provided the links.

Walpurgisnacht, Johannisnacht (Wikipedia does not mention fires, but here are photos from “More Than Beer and Schnitzel.com” ), and Martinsfeuer link goes to a random youtube video with a fire (There were enough bonfire related images in my search for Martinsfeuer that either that word means “bonfire” or there are a number of bonfires during that festival).