I’ve been digging around in the Knowledge base and support forums, and I don’t see this questions addressed.
Is it allowed to create a single theme and sell it simultaneously on multiple platforms; WordPress, Joomla, Drupal, etc.? Is there a limit on how many platforms a single theme may be developed for and sold on?
Yes you can
you can sell your theme on each platform available with no problem. The more platforms it is accepted on, the easier it will get through with the next review.