In my experience it is the drivers door lock actuator at fault. This is also a part of the door clasp that holds the door shut. Likely the motor or thermal fuse inside this has failed. It's not overly expensive as a replacement item. Looking at between $45-$115 depending on where you purchase it.
On this website you can select the year make model of your car and it will show you videos for different items.
https://www.1aauto.com/videos
Also this generic youtube video gives you an overview.
flat battery in the fob
broken power wire between the door hinges
faulty door lock actuators
faulty master control switches
or faulty door switches at the doors