Thanks, but as I noted in the original post command backslash does NOT allow a search when the disk password window is active, ie when you've clicked in it. One can use command shift space to bring up the search, and then arrow to say a password, but when you use Shift return you get a dialog asking "Would you like to link your "[name of volume]" item in 1Password with your macOS user account login?" the only options are fill once, fill and update login, or cancel. None, as far as I can tell, will lead to the correct password being filled in. And it would be a bad item to have my drive passwords be the same as my system password.