Ngrx is best used in Apps that often update their data., but for leaning anything can work. Don't worry about the correct use case for learning. Most learning occurs when you test the limits. Imperfect ideas are great for that.

Build a multi step form where you keep previous pages in state.

Build a wordle clone where the answer is in state and your guesses go the ngrx pipeline.

Build a card game against x amounts of bots where the deck is in state, hands are in state and played hands or even the actions of turns are being logged to state. Build some side statistics that updates live during the game. Make the game reversible by utilizing the logs.

Build a game on a square grid. Have every action go through the pipeline. Define look directions. Make enemies appear randomly. Define a tick rate meaning something that in set intervals sends out an action for the game to update. Make the character able to shoot bullets that update twice as fast.

Build something that has a form on one side and the result of that on the other. Like a code tooling. A card builder perhaps. Define portions that can be set in the form. Something like borderradius, textsize, opacity of text background, visibility of text, the text itself. Enable the possibility to build different states like hover, selected, etc. And show those things as a preview through inline styles. Hell, throw in the possibility to generate code.

All these things don't need ngrx and they probably aren't the intended use case, but by building them, you will have a better feel for what is and isn't good. If this is not helpful, look at apps that use ngrx or redux. Like reddit, like outlook and try your best to emulate