Unable to reply in apple discussions

As H1290 points out, the banner means the thread has been locked due to age or inactivity, which makes sense to me. In my long tenure here I have seen very few posters who come back weeks or months later to look for new responses to their threads.

Note that the thread you tried to reply to is over three years old; that's a trilobite in forum years.

If you come here from a search engine, there's the problem. You will see far too many of those banners. Search engines are not conducive to effectively helping here because they do not show locked v. active threads.

The better way to help here: 

—Bookmark this forum site map: Site Map - Apple Community

—Choose topic areas where you feel you can best help. 

—Use the site map’ topic links to go directly to those topics.

—Work the first few pages with the newest posts. 

That gives posters the most current information, and they can recognize your contributions with an upvote.

Hello!

That’s an old post that has been archived. Old posts are archived, and no one can post in them after that.

If you see this banner (with a red arrow in screenshot) you’ll know the thread is locked. Also by the disabled reply buttons, of course.

Have a great day!