I have enabled Animation Looping in animation player and made sure it’s saved in a resource file. I verified it in another scene so things worked perfectly.
However, once I deleted .godot folder (you know, not frequently but once or twice per month?), the flag went back to disabled.
Deleting the .godot folder isn’t an oil change - it’s a catastrophic recovery method. Doing it once or twice a month means you have other problems you need to solve another way.
If you set an animation to loop on the Advanced Import Settings it should stay looped.
You can create an Import Script to loop selected animations and attach it to a file for import. That will re-apply the looping every time it is re-imported.
Sadly the “save to external” option does not keep track of changed settings, and will be overwritten with each import, since others, or yourself from another computer may work on the same project it’s a good idea to only change import settings or use an import script. The import setting “Loop Mode” does specify if the animation should loop, ping pong, or play once, which does include whether or not looping is enabled.