Learn Russian: Мы возвращаемся домой в пятницу.

No. While this lesson focuses on passive reflexives (like дом строится - the house is being built), the -ся ending here just makes the verb intransitive, meaning the action is focused on the subject. Instead of returning an item to a store, we are returning ourselves.

Why is the present tense возвращаемся used if the event is happening in the future?

Just like in English, Russian frequently uses the present tense of imperfective verbs for planned or scheduled future events. You could also use the future perfective here (мы вернёмся), which would put more focus on the result of successfully getting back.

Why does the sentence use домой instead of дома?

Дома means 'at home' indicating a static location, but returning implies motion towards a destination. Домой is the specific directional word for 'homeward' or 'to home', which you must always use with verbs of motion or direction.

Why is the word for Friday (пятница) ending in -у here?

To say that something happens on a certain day of the week, Russian uses the preposition в followed by the accusative case. Since пятница is a feminine noun, its -а ending changes to -у in the accusative case.