How do I find my last postings?

Or bookmark this: Bicyclesnowplow’s Subscriptions - Apple Community

Note the "Filter" option near the top:

Setting "Recent Activity" to "Authored" from the default of "Following" shows threads you started.

Bicyclesnowplow wrote:

Doesn't seem there's anyway to keep track of postings

Check by clicking on your profile icon at the top right of the forum, then select my subscription.