K9 suddenly wants to encrypt all mail, and won't send any

Obviously, I have inadvertently changed some setting, but can’t figure out what. I use K9 with 6 accounts, none of which have previously used encryption (I would prefer to – my correspondents wouldn’t). Suddenly all of them, when I try to compose an email have a red padlock at the top right and a tooltip appears at the bottom saying > “Cannot connect to crypto provider; check your settings or click crypto icon to retry”. On the individual account settings, and also on global settings, the Cryptography tab shows : - OpenPGP App - None - Show unencrypted signatures – unchecked - Autocryptography Mutual Mode – unchecked. I cannot find any other cryptography options and do not remember changing any. What *might* have caused it (a very slim chance, but I can think of nothing else) is that it first occurred when I used FireFox Focus, which is privacy oriented and always runs in private mode, to share a link to a web page. Perhaps that changed some setting? Well, it doesn’t really matter how it happened, but now I cannot send any mail without this error message. How can I disable cryptography in K9?