Every time a Moon mission comes up, Helium 3 gets trotted out, but it's just absurd.
For one, billions of tons of rock would have to be mined to extract any reasonable amount of Helium 3. Even with heavy machinery and robotic miners operating 24/7, this is a stretch.
But much more importantly, Helium 3 is utterly useless. It was proposed as one possible fusion fuel but then a much cheaper alternative was developed almost immediately: breeding the required fuel from a blanket of Lithium.
Last, but not least: There are exactly zero fusion power plant operational on Earth right now. There will be exactly zero commercial fusion power plants operational on Earth for at least a decade, no matter what new technologies are developed. At the current pace, according to current plans (e.g.: ITER/DEMO), there will be one (1) power plant generating a trivial amount of power staring in 2048. Likely well into the 2050s there won't be many more.
So to summarise mining lunar He3: We should spend trillions of dollars digging up the Moon for power plants that won't exist for three decades and don't need need the helium anyway.