Finger fatigue suggests you're holding tension in your fingers and wrists. A good teacher can help you with that. You need to learn to keep your fingers and wrists as relaxed as possible - which is unbelievably hard to do when you're also trying to learn how to read music.
Watch some slow piano music being played by a concert pianist, and you'll see that - except for the odd flourish - they move fingers and wrists as little as possible. The hands float, they don't hover in a tense way.
It also depends on the keyboard you're using. There's a big difference between a soft and fast keyboard action and a piano action with real or simulated hammers. The latter is much harder on your fingers to start with, but gives you more control and stamina later.
your last point is spot-on; I have a decent yamaha electric piano and the action is quite a bit heavier than my sister's Boston acuostic. It's not suprising but still notable how much more fatigued you feel after an hour of playing mine vs. hers.
Watch some slow piano music being played by a concert pianist, and you'll see that - except for the odd flourish - they move fingers and wrists as little as possible. The hands float, they don't hover in a tense way.
It also depends on the keyboard you're using. There's a big difference between a soft and fast keyboard action and a piano action with real or simulated hammers. The latter is much harder on your fingers to start with, but gives you more control and stamina later.