When you select one of the replies as the best answer to your original question, it will change the topic to Solved.

I don’t see a way to easily see the topics you’ve created and sort them by solved. You can see a list of all your topics from your profile:

and when you’re there, you can see which ones have a check mark by the topic:

but I don’t see a way to filter with a “solved” drop down. Does this get you close enough or would you like me to raise an idea with the platform?