Is it permissible for a Muslim residing in the West to deal with banks, open businesses, and purchase real estate, based on the premise that these transactions are considered void contracts because they are with non-Muslims?

The ruling on usury in non-Muslim lands is the same as its ruling in Muslim lands. This is the view of the majority of scholars, and their evidence for this is the numerous Quranic texts and prophetic traditions that prohibit usury without differentiating between the land of war and the land of Islam, or between a Muslim's dealings with another Muslim or a non-believer.