Can't relaunch/use finder on a 2019 MacBook Pro
When you relaunch Finder, are you doing this from the Force Quit Applications menu? If you haven't done this, try pressing command+option+esc keys and the Force Quit Applications menu should pop up, then relaunch Finder from there.

If this fails, you can also try force a reboot by pressing Control+Command+Touch ID/Power button keys.

If this also fails, and you have access to Spotlight, search for the Terminal app. Once in Terminal, you can force a reboot by typing sudo reboot. It will prompt you with your password, but it won't show in the terminal window as you type it. Just hit the return key when you've finished typing your password and it should force your MacBook to reboot. 

Hope this helps.