What is the ruling on purchasing an apartment in a residential complex that requires paying periodic fees to the owners' association for the maintenance of facilities (swimming pools, playgrounds, central satellite dish), knowing that the owner only watches on television what pleases Allah? Is he sinful if other owners watch what Allah has forbidden?

Paying maintenance and service fees to the homeowners' association is in exchange for benefiting from the common amenities of the property. Your lawful use of these amenities is not affected by others' unlawful use, for each person pays for their own benefit. Allah Almighty says: ﴿And every soul earns not [anything] except against itself, and no bearer of burdens will bear the burden of another.﴾ If it is possible for you to have your own private service, that is better. However, if sharing is a mandatory general system for the complex, then there is no blame.