Safari

Go step by step and test.

   1. Check for adware.

       Run the latest release of Malwarebytes for Mac to remove malware/adware, if installed on your Mac.

       For instructions: Install Malwarebytes for Mac v4      Uninstall Malwarebytes for Mac

       Click the “Scan Now” button. Once done, quit Malwarebytes for Mac.

       Restart the computer and relaunch Safari holding the shift key down.

       Scan for Malware again.

2. If this doesn't help, hold the "shift" key down, click the  in the menu bar and choose "Force Quit"

Launch Safari holding the shift key down.

3. Startup in Safe Mode   https://support.apple.com/lv-lv/HT201262

To exit Safe Mode, click the Restart button at the bottom of the screen.

If the above doesn't work, shut down the computer using the power button and then restart.