You should be able to:
sudo rm /lib/firmware/rtlbt/rtkbt
Check if you have a /lib/firmware/rtkbt. IF you do, remove that, too.
In terminal, run:
sudo apt install --reinstall blueman bluez-utils bluez bluetooth
sudo /etc/init.d/bluetooth start
Launch Blueman from the app menu, and try pairing the Bluetooth keyboard.
COEX_v0202$ sudo rm /lib/firmware/rtlbt/rtkbt
rm: cannot remove '/lib/firmware/rtlbt/rtkbt': No such file or directory
Can you please open a File Manager.
Let's see... you are on Pro - so that is Nautilus...
sudo -i
nautilus
Other Locations from the left pane, then "computer" then lib > firmware > rtlbt
Look in that folder and see if you find any file or directory named "rtkbt"
No i dont have any directory named "rtkbt" there.
Maybe that driver did not fully install... :
Can you follow the next steps outlined above and relay the results?
You mean these commands? >
sudo apt install --reinstall blueman bluez-utils bluez bluetooth
sudo /etc/init.d/bluetooth start
root@CrocsT480s:~# sudo -i
root@CrocsT480s:~# nautilus
** (org.gnome.Nautilus:5931): WARNING **: 20:44:24.895: Unable to get contents of the bookmarks file: Error opening file /root/.gtk-bookmarks: No such file or directory
** (org.gnome.Nautilus:5931): WARNING **: 20:44:24.895: Unable to get contents of the bookmarks file: Error opening file /root/.gtk-bookmarks: No such file or directory
Nautilus-Share-Message: 20:44:25.007: Called "net usershare info" but it failed: 'net usershare' returned error 255: net usershare: cannot open usershare directory /var/lib/samba/usershares. Error No such file or directory
Please ask your system administrator to enable user sharing.
This is only because the plugin looks for your Bookmarks from the Home Directory, but you just launched Nautilus as the Root Directory.
It can be ignored.
Ok, easiest to reinstall or?
I do not understand the question...
If its not possible to repair/fix maybe its easier to reinstall Zorin again?
Oh, I see. Yes, that is an option and if you are comfortable with that option, you can do so at any time.
Thanks for all the help. I appreciate it.
Good news. After i installed bluetooth is working as it did earlier. Another good thing is that i can use my NAS542 now to access files etc. One last good thing is that bluetoth found my Logitech K810 keyboard 
It was worth a reinstallation. Thanks once more for the time you spend on helping me.
Sometimes, a reinstall works wonders. 
I actually often prefer to suggest it... but most users balk at the idea and really want to troubleshoot all the way through...
I applaud your lack of reticence.
Make Back ups Often, in case you need to wipe and reload in the future. I also usually prefer a reinstall with a new Fresh Start as opposed to trying to untangle whatever I did...
Can you suggest a good backup program?
Zorin comes with DejaDup Back Ups. Many recommend Timeshift. I, personally, use neither and just back up what I want to keep manually.