From Mojave onwards it’s no longer possible to get the 1 Password app to automatically entering your passwords into a webpage. Previously there was a keypress that would automatically fill a web form and enter your password and then press the submit button.
According to the one password forum this was disabled by Apple:
This is a limitation that’s being imposed by Apple in Mojave — though to be clear, it’s one we don’t disagree with. Auto-submit was always a sort of tacked-on feature. Auto-FILL should still work as it always has (in fact, it should be better than ever), but in order to accomplish auto-submit in previous versions, we had to use a small script that simulated the actual pressing of the Enter key. Apple – quite rightly, in my view – pointed out that this is the identical mechanism used by some malware to install itself — it can’t actually press return on your computer for you, so it simulates that action with a small script.
Strangely, even though 1Password is not allowed to press the ‘Return’ Key, Keyboard Maestro is still allowed to. A workaround I have found is to use a keyboard maestro script to execute 1Password and then press the Return key for you. I have written a script that calls up 1 Password and then simulates pressing the key for you. I have mapped this to a function key so now I can have a one press solution to bring back the old functionality of 1 Password prior to Mojave.
Here’s what the script looks like in Keyboard Maestro.