Is it permissible to pray in a mosque consisting of two separate floors, especially for Friday prayer, with the presence of a loudspeaker?

There is no harm in praying in a two-story mosque, whether for Jumu'ah or other prayers. The upper floor is considered an extension. There should be an opening between them near the Imam to hear the sound when the electricity is out, and the delay of the congregants behind the Imam should be noted.