Some *.blend files carry geometry nodes, others don’t. All the settings generate looping animations.
Minimal level: intermediate.
Tested in Blender 3.3.1 LTS and Blender 3.4.
In both the shader and geometry node editors, the light gray nodes are recommended to animate. However, some nodes are responsible for the looping process, therefore, please, be careful with what you do. Even some Color Ramp nodes carry animation triggers.
Most of them carry compositing.
Please, always keep the original files, in case of messing up some settings, thus in order to keeping clean starting points.
You may not only use those files' settings to raise your Blender level of knowledge, but also to use, adapt, those blend files within your own creations by tweaking them.