For road riding you don't need more than 700 lumens, unless its a very dark night and raining then you could use 1,200 lumens.
But for MTB riding you need about 50% more power unless you're doing fast downhill stuff than you'll need twice the power that a road bike will need! And you need to know how long you will be out because that will dictate what run times you need to be looking for.
You should also consider, whether road or off road, using 2 headlights, one on the bar and one on the helmet.
If you are not doing the fast DH stuff then you need to look for lights with 1,000 lumens on the medium setting to 1,800 lumens on high. DH lights are horribly expensive, running at around the $450 price range.
Word of warning, not all lumens are the same, one company might say they put out 1,000 lumens but it could look like someone else's 500 lumen light! So now what do you do? Well, you can go to this website and compare side by side with a lot of various lights on the market, this site will show you just how dim a lot of lights are even though they say they put out huge lumens. In that light comparison play close attention to the NiteRider Lumina Max 2500, it pretty much beats out all the lights, but whatever light you decide you will have to go to the company's website and find the battery run times.
https://road.cc/content/feature/roadcc-front-bike-lights-beam-test-310999