Is it possible to do transparent meshes with blend modes, like this?

Add/addition mode in image editors and game engines looks like this. When shapes overlap, it gets brighter, and dark colors are not visible.

Is it possible to do transparent meshes with blend modes, like this?

Add/addition mode in image editors and game engines looks like this. When shapes overlap, it gets brighter, and dark colors are not visible.

Edit: So as you've reformulated your question it looks like my answer is not correct anymore, anyway I leave it as it is.
If you're talking about the light beams, here is what you can do:
It's a ColorRamp plugged into an Emission that goes on the Z axis. Also you need to put a transparent gradient and some noise. Don't forget to go into the Material panel > Settings and Blend Mode > Alpha Blend:
You can transform the shape with a Lattice modifier for example.