Is the profit from providing Internet broadcasting to subscribers considered lawful (halal) or unlawful (haram), given that I cannot monitor the content of their browsing?

The fundamental principle is the permissibility of selling and renting services and benefits that can be used for both permissible (mubaḥ) and prohibited (ḥarām) purposes, unless it is known or highly probable that they will be used for something prohibited. If the predominant use is prohibited, then selling them becomes unlawful, based on the statement of Al-Shawkani regarding the prohibition of selling anything whose benefit is exclusively confined to something unlawful, or whose predominant use is for something unlawful, or which is intended to be sold for use in something unlawful.