Remember: While changing animation, always add a Trigger Once condition so that it doesn’t change animation every time without giving the animation to get played.
Search for it in the event editor, on the condition site.
But you don’t want to use a trigger once here.
The probem is your idle and run event is true at the same time.
That used to be an issue, but now if you set the animation to what it is already, GDevelop seems to ignore the action and keeps animating.
@Blast-Forever, what @jack means is the two conditions highlighted below are both triggered. So, the animation is changed to “idle”, and then immediately to the first frame of “run” :