I am constantly getting double characters when I type in the “Insert Action By Type” search field. This is the only place I am experiencing the issue… in any program.
Hmm… this keeps happening to me. Based on the silence, it must not be happening to anyone else.
Maybe if you can do a video/animated GIF showing the behavior we could be of more help. I have not seen this behavior myself.
While making the video I realized it happens if I backspace while typing in the search field.
I think you may have some text expander tool at work here, like the System Preferences > Keyboard > Text, TextExpander, KM, Typinator, etc.
No, nothing like that. It does the same thing on my home and work computers.
Then you might look for what common between your computers that could affect typing.
I’m afraid not. As suggested, it appears to be some sort of interaction with some other software. Since you have it on two Macs, that indicates it is something installed on both those Macs, so maybe that gives you a clue.
You could try creating a second account and see if you have the issue there, that might give you a clue.