Estimating a number is difficult, as most retail users store their BTC with a custodian/exchange. Coinbase alone has 30 million users, for example. Either way, pretty much every research available on the matter will show you a number definitively in the millions. Holding, speculation, trading are all usage scenarios for a SoV asset like BTC. As for "monthly active users", it's definitely much less.

Brave is basically a reskin of Chrome (Chromium), except with trackers and ads disabled. It's definitely faster than, or at least as fast as, Chrome. Give it a shot, it's a really good browser that puts privacy first.