Can we have mixed gatherings in the community center next to the mosque?
Is it allowed to have a community center next to a mosque with a shared parking lot where Muslims can meet for social gathering, dinner, education, children activity, sport, swimming, music event but some Muslims ( male or female) may not fully comply with the Islamic dress code or may not perform the daily prayers ( believers but Sinners)?
Yes, this is permissible so long as it does not lead to anything prohibited by Islamic law.
According to the practice of generations of Muslims from among the predecessors and successors, the mere presence of males and females in the same place is not prohibited in itself. Rather, the prohibition concerns the manner of their gathering if it contradicts the rulings of Islamic law. This includes, for example, women uncovering what they have been commanded to cover in Islamic law, gathering to commit an abominable act or sitting in unlawful privacy with the opposite sex. As for the prohibited mixing between the opposite sexes, it is that which involves touching and physical contact and not merely being present in the same place.
It is permissible to attend such gatherings and none will be blameworthy except whoever exceeds the limits of Islamic law. However, it is impermissible to attend if one fears from temptation [fitnah].