The title pretty much explains what I want to do.
As far as I know, there isn’t a place that is designated for solutions - probably here on the forum would be the best, or perhaps making a youtube video for the freecodecamp channel, or a medium article on how you solved it. You could look around on the forum for a topic that involves that challenge as well.
You could post it here, marked with a spoiler (some people might want to try to work it out themselves).
You would probably enjoy codewars if you like doing algos.
Creating videos that walk through how you solve the challenges could probably help fellow campers. You may also enjoy contributing to The Guide. This isn’t intended to hold challenge solutions, but to be a user-friendly resource for campers. Most of all, you can spend time here on the forum. Look for people asking for help with challenges you’ve solved and help them find their way to a solution.
As @ArielLeslie points out, the main purpose of the forum is to help those campers who are struggling with a challenge. See if you can use your knowledge of the challenges you have solved to “guide” a struggling camper to a solution. Do not just post your solution, but see if you can give small hints, suggestions (i.e. references to documentation), or provide short code examples of a specific topic which might help the camper to “realize” where to take their own solution to pass the tests. It is always much more rewarding to solve a challenge without first seeing the complete solution.
Even if you mark a solution with a spoiler, it is sometimes too tempting for a struggling camper to not take a peak and miss out on figuring out his/her own path to a solution.