To find all threads you've made, you can go to 'My Topics' on the website. Your most recent threads you've created also show up on your profile, but only on the website.
To find all the threads you've posted on that you didn't create, you can use the 'follow' tool on threads. I believe that unless you turn the setting off, you auto-follow any thread you post on.
But... all of this is only on the website.
How can I find threads I’ve started and/or contributed to? Is there an archive? It’s so easy to lose track.