Code:

		
			/*:
 * @target MZ
 * @plugindesc Fully restores HP and MP when a character levels up.
 * @help
 * This plugin automatically restores a character's HP and MP to full
 * when they level up. No configuration required.
 * 
 * Free for commercial and non-commercial use.
 */

(() => {
    const _Game_Actor_levelUp = Game_Actor.prototype.levelUp;
    
    Game_Actor.prototype.levelUp = function() {
        _Game_Actor_levelUp.call(this);
        this.recoverAll();  // Restore HP and MP
    };
})();
		
	

This was made by ChatGPT because I needed one for The Flipside and couldn't find one that wasn't paid or didn't need me to reach out to the plugin creator.

The way you get this working in RPG Maker is by copying this text into a note document and saving that note document as a .js file, then putting it in the plugins folder of your RPG Maker project.

I don't know the stigma around using AI-made plugins for a game. I have a heavy dislike for people using AI-made art and music (though I have done it myself once).

Enjoy!