If there was a thread that was closed it is either because the core issue originally reported in that thread was resolved or the thread had diverged from whatever issue was originally being reported and became toxic or no longer constructive.
Low FPS has so many potential causes that it isn’t safe to just assume that since there was another thread at one point, that your causes would be the exact same as the original poster in the other thread.
Additionally the community can’t offer more than very general advice if you do not provide any details, any system information, any context to your post.
If you are looking for troubleshooting assistance with an issue, go ahead and follow the steps here then reply back with more details about what you are seeing, when/where it happens, and what, if anything you have already tried to resolve it.
If you don’t wish to do that here, you can submit a ticket for direct Blizzard assistance. Click your name, click support, click contact support.