I am seeing similar behavior - the iCloud Passwords extension no longer shows as a drop down in the username/password field on websites. I can get it in the menu bar icon but can frequently take two clicks to get the password to show. Occasionally I need to reload the webpage and then the menu icon will show the password item. I do not have any problems "activating" iCloud Passwords - I always get the 6 digit code to authorize iCloud Passwords.
Since this problem has been occurring I also have no way to get the 2FA codes since the drop down in the 2FA field is not there and the menu icon does not show 2FA codes.
1Password does still work in the username/password field on websites.
I am on the latest release version of Tahoe - 26.1 on an intel Mac Pro 7,1 with Orion RC Version 1.0.0 (139-rc), WebKit 623.1.8.0.0. I see the same behavior on Orion as well.
I have tried both the verion of iCloud Passwords from the Chrome and Firefox Stores.