In the ongoing work to replace overly rigid Forem concepts with more flexible building blocks, the "sponsorship" functionality is officially being removed soon.
This has been deprecated in the past and is generally no longer functional, but it will officially be removed soon as to eliminate all possible confusion.
Pretty much anything that was possibly done through the hardcoded "sponsor" functionality is achievable through "Display ads" and "Pages" in ways that allow for much more administrative functionality. Therefore the specific dedicated concept of sponsoring a Forem is being removed in favor of functionality that allows that to be pursued in ways that are most useful to that Forem.
This ongoing clean up work is having a really positive impact on our capacity to invest in the most impactful functionality in the platform!