How many months before a post is no longer accessible?

Yep you have to have a search term and then you can filter the results by the Author of the post. Using your name as a search term only brings up the posts that include your name in the text of the post. That will also be the case if someone quotes a post of yours as it would show your name in the post as this:

ehsup wrote:

ehsup wrote:

I posted several questions less than 12 months ago on Apple Community. I no longer find those questions when I log into my account. I do not see a way to change the filter away from "Recent Activity". Is there a way to see those posts or did Apple purge them? If deleted, does Apple delete all posts after a specific time period, or is it because I have not logged into this account in over 6 months?

There are two ways to look for those older threads. One, use the built-in forum search feature and search by your username. It appears you've found that.

The other way to search is through an internet search engine. Use this search term:

site:apple.com ehsup

I see several post by you here where the search found the word "iPhone"

https://discussions.apple.com/search?q=iphone&page=1&perPage=20&content=filterDiscussions&author=723baf7937fb2fda&sortBy=relevance&source=aml&origin=asc_serp&searchId=rZ9vWYaATVyJnmTumVzPjw

When viewing the Subscriptions in your profile, you will only find the posts that you have subscribed to and that is indicated by the solid blue bell on the bottom of the original post. By tapping the bell, it will unsubscribe and no longer appear in your subscriptions.

Tap or click up in your profile then go to my subscriptions you can find everything you have posted in the forum