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.

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

Enjoy!