A mind–reading brain implant that comes with password protection

This. It's like if you want to collect biometric data about everyone's faces with different expressions, different angles, and how those faces change over time, you just make a mobile app where people voluntarily record themselves.

So, if the problems are:

>> It requires several electrodes to be implanted into the patient first. Then there's an adaptation phase in which the patient trains the system.

Then one possible way I can think of to make people do your work for you, is to release a nice VR videogame to the point it becomes popular, and have some features that make it nicer if you ("enhanced controls", or "your HUD shows exactly what you want just by thinking it like Ironman helmet", or whatever).

Taking an existing and popular videogame and making a mod like this would also work.

There's non-zero desire for full-dive MMORPGs, so marketing it like a step towards that would entice a non-zero amount of gamers.

Once it's normalized on niches like that you'll probably have a better time expanding outside that niche, because by then it would be "that videogame tech thingy that cool and rich streamers use" rather than "the sus mind reading stuff".

It doesn't need to be videogames, but the idea is the same, you make an "inoffensive" thing that people want to use, and then leech off the collected data.