I am using TB 115.8.1 on Ubuntu. I had set up an openPGP key for my main address but never used it. When I created templates to use for OoO as per https://support.mozilla.org/en-US/questions/1126211 I found that the OoO reply messages (even for a different address) were attaching the key. Stupidly with hindsight, I deleted the key. Now I find that many but not all the messages in my saved folder won't open as TB says, correctly, that the key is not accessible. However, I never asked TB to encrypt these messages. I also still can't get an "Autocrype: addr=" out of the replies using some of the OoO templates I created. At least for me the openPGP is pretty fundamentally broken and has lost me content and time. I like TB but this is seriously frustrating. Perhaps this is a useful warning to others.