I see what you mean. But what I don't understand is that if it says the max height is 400M then why does it allow me to get to that height? Saying that the flight path where I am I do t have to worry as the planes fly at around 2600 feet so I have no worries going to the height I go
For clarity you should include MSL (mean sea level) and AGL (above ground level) when talking about this stuff, so there is no misunderstandings in posts.
400 feet AGL is your advised highest altitude you should fly drones, you should know that, right? In general terms most manned aircraft are above 500' AGL, but there are exceptions, hence having visual line of site (VLOS) is important to avoid conflict. You can set your RC GO app settings to limit you to 400' help you avoid flying higher if you wish, but I usually stay below 300' AGL. However, I will often set mine to max height (500M) and fly over 1000' above my home point, but I will stay below 300' AGL. This is because I'm going up a mountain. That's why the GO app allows up to 500M (1640') of ascending from home point.
So, with GO set to allow 1640' (500M) AGL, how do you know if you're below 400' AGL while climbing a mountain (you might be thinking)? Experience, that's the only way. You need to stay low and judge your altitude through the display. Judging elevation through the display is actually easier than VLOS in my opinion. The view in the display at 400' versus 100' AGL is easy to discern with a little testing and training in the field.
To learn about elevation estimating through the display, there's a little game to play with yourself
on level land. If you're flying on flat land that's the same elevation as your homepoint you can train yourself on elevation estimating. As you're flying along for run, fly up to 400' AGL and memorize the display look. Then, WITHOUT looking at the elevation telemetry on the GO screen, descend to an elevation that YOU BELIEVE is 100' AGL. Then look at the elevation telemetry and see how close you are to your visual guess. After you do this about 25 times you'll learn what certain elevations look like. BTW, this changes if you fly a Mavic with a different FOV camera.