Omnikey for Safari 13?
I was totally bugged out by the lack of Omnikey after upgrading to Safari 13.
This applescript saved my life (it's not mine so I'm just posting the link):
https://macscripter.net/viewtopic.php?id=47107

In order to activate it, open Automator, create a new Quick Action, select "Run Applescript" from the action list on the left side of the window, and copy/paste the script to the editor window. Above the editor window, change "Workflow receives" to "no input" and save.

Then go to System Preferences, keyboard, shortcuts, and assign a keyboard shortcut to it. Now, when in Safari's address bar you can just press the shortcut and the script transforms the search to the right URL, e.g. type "we apple", press the shortcut, services, and the wikipedia article about "Apple" opens in the same Safari tab.

In order to add more searches, just edit the script in the "property shortcuts" section, it looks pretty self-explanatory to me. Now searching from the address bar works almost as before, just have to get used to pressing the shortcut instead of return.