97 Hyundai Elantra driver side door failed to unlock from inside or outside. The key was a little stiff in the driver's side lock for a while and then refused to unlock the door. It feels as if the door unlocks but then the handle acts as if the door is locked from both inside and outside the car.

You will need to remove the inside door panel, what that takes I don't know, but it must come off to access the door latch, there you will likely find the latch release control rod has come off or the latch is defective.

Fix your car right away by clicking the link I attached https://www.reliable-store.com/products/2004-hyundai-elantra-repair-manual

check your battery in key

door lock actuator might be faulty or bad electrical contact
take off the door panel and diconnect and reconnect the wiring, you might need to change door lock actuator

Same thing happened with mine. It turned out that the power door lock motor went out. Since the handle or the switch can unlock the driver's door, both of these mechanisms are connected. When the door lock motor goes out it freezes in whatever position, it was last engaged.

yes

take an old auto antenna or, a very stiff metal rod and, using a plastic blade (like a plaster knife) bend the glass on the driver's side door; at the top of the door; gently outward; place a rubber or, wood spacer (eraser, wedge etc) between the door frame and, the glass: you only need one inch space; use the rod to press /pull the button / lever on the passenger side

Sounds to me like the child locks are on. Make sure the doors are unlocked first( if they are power locks unlock them manually to make sure they are unlocked), then try to open from the outside. It's just odd that both doors are doing the same thing. If that works, and you get both doors open, there is a small switch to disable the child lock near the latch on the door.

Door panels generally can not be removed with the door closed. There are plastic rivets that pop out when pulling the door panel away from the door frame.

Try spraying some type of lubricant like wd40 in the key hole and using a small metal pick to dig the broken part out. You can also use skinny flat piece of metal like a nail file and place a strong magnet on the end of it with any luck it will grab the broken piece of key. Good Luck

There is a "bar" that attaches to the lock like a lever pulling and pushing the door. Over many years and hundreds of unlockings it breaks from the plastic...I am in the same boat. It won't cost that much....take it to the dealer..the part is around $13.00 to replace