Wa alaykum salaam
Saying jumma mubarak is not bidah according to the School of Ahl al-Bayt (as). While the specific words jumma mubarak are not found in hadith reports, it is a prayer for the person to whom it is addressed and falls under the general recommendation to pray for your brothers and sisters in religion. Friday is a day of multiplied blessings and a day of worship, good deeds and good will.
May you always be successful