So, when you’re working on the normal inspector, by default, it doesn’t keep the changes that you made in PlayMode. This doesn’t happen when working with a custom inspector, does anyone know how to “fix” it? It’s a pain to reset everything manually after every testing
No, that’s not true. A custom inspector (when created correctly) behaves just like the normal inspector when it comes to serialization. However it depends on what you are inspecting / editing. Objects in a scene will be reverted when you leave play mode. However any changes to assets will persist. So if you edit a Material, Texture import settings or prefabs (the actual prefab, not an instance in the scene) those changes will persist.
Do you have any more context about your issue? What are you editing?