Why can I not answer an old question?

Have you tried:

Open the most recent message asking the question.

Copy the question.

Open a NEW 'Ask the Community' question form.

Give it an appropriate name.

Paste the copied question into the new message.

At this point you could either answer the question (and add a brief message explaining why you are answering a question you have just asked),

OR post the question, then answer it in a second message.

OR post the question, wait for 12 to 24 hours, then post your answer as a reply to the question.

Not something I'd recommend (or do) in ordinary cases, but it could prove useful under the circumstances you describe.

Regards,

Barry

Community questions become read-only after some Apple determined lapse of time.

Regardless of Preview, Pages, Numbers, or Keynote, once you manually save a document once, then autosave is enabled and will only happen every few seconds when it determines changes are in the buffer. Autosave cannot be disabled from within these applications.

However, you can prevent autosave with System Preference/Settings changes.

Ventura

System Settings > Desktop & Dock : Windows & Apps : Ask to keep changes when closing documents (=⦿)

Monterey and earlier

System Preferences > General : Ask to keep changes when closing documents

You will see a black dot appear in the above applications red titlebar icon indicating that no autosave is operational and you will be relegated to manual saves which will temporarily clear that black dot in that icon. There is greater risk of losing data using this configuration than the autosave protection.