Given that it’s presenting as a mechanical issue, the key would be the best place to start.
Take a good look at the key for starters, are the parts that should be pointy still pointy? The cylinder, while not a precise instrument, operates on a system that requires the key to fit properly to engage the pins so the cylinder turns and engages the switching mechanism.
If the key looks worn, you should be able to go to a local Ford dealer and get a key cut from the VIN. Having a duplicate made may not correct anything. However, replacing the key may mean you’re paying for the immobilizer to learn the key, or go ghetto and put the old key under the column cover. Simply getting a key cut should allow you to test if the key is the issue by seeing if the key now does what it has to so the key turns.
If something inside is physically sticking, you could try giving it a shot of a dry graphite lubricating spray and nothing else.
If neither of those yield results, the nest best step would be to take a peak inside and make sure any interlocks are disengaging fully before you shoot the parts cannon. If there is an issue with the cylinder itself your local locksmith would be a better option than replacing the cylinder itself and having 2 keys for the car.
Sorry for the long post, I’m having flashbacks of replacing GM cylinders before the recall, mostly because of “20 lb keychains”. It’s also something that diagnosis is based on the very qualitative feel of trying to insert and turn the key.