How do I fix my phone?

@ilijastefanovic first thing to always try is a soft reset. Hold the Power button until your phone shuts off, wait 30 seconds, and then turn it back on.

After that, try to start your phone in safe mode. See if that responds.

Last resort is a factory reset:

Please follow the instructions below to factory reset your Samsung in recovery mode if you cannot access your phone’s factory reset options in regular mode.

1. Hold down the Power, Volume Up, and Bixby/ Home buttons simultaneously.
2. When the Samsung logo displays, release the buttons and wait for sometime for the device to enter recovery mode.
3. Use the Volume buttons to go through the choices, then the Power button to choose “Factory Reset/Wipe Data.”
4. “Factory data reset” may be selected by pressing the Power button after pressing the Volume down key to highlight it.
5. When the factory reset process is finished, press the Power button and choose Reboot System Now. Watch for the computer to restart.

You may have to reflash your software with Odin if none of this works.