You can appreciate what a job taught you and still know it no longer fits.

Gratitude and fit are separate questions, though they often get argued as one. A place can have shaped you honestly, given you skills and people you would not trade, and still be the wrong room for who you are now. The pull to stay out of loyalty is real, and so is the guilt that comes from wanting something else. Neither of those is evidence that leaving would be ungrateful.

Try writing down what the work actually gave you, plainly and without hedging. Then write what you now need that it cannot provide. Reading both lists side by side usually makes the next decision quieter.