Transmission does not shift into fourth gear?

More then likely this is the torque converter clutch solenoid or the converter itself has failed.

We need to start with checking for codes and go from there.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Once we know if there are codes or not we can go in that direction. If there are no codes then we need to follow the testing information below to try and confirm the converter is the issue. However, this is what I suspect the issue is.

Let me know if you have questions. Thanks