Find all my questions

Each user has a Profile page.

Your Profile page lists your topic ‘Subscriptions’.

You can filter your topic ‘Subscriptions’ on the left side, by choosing ‘Participated’ or ‘Authored’.

If that doesn’t list what you expected, then those missing threads are old, or the site Search is misbehaving.

You can bookmark that search result page for easy access at a later time.

Your topic subscriptions at Apple Community

Alternatively, try what third party search engines know about your posts on this site.

"MartinLiss" site:discussions.apple.com - Google Search

Not sure why site search is worse for your profile than for some others. You can give feedback to Apple (mention Apple Support Communities Search), but I think the devs are aware that forum Search has some issues.

In the meantime, I hope that the Google alternative helps you out for this.