Here is a quick tip to have alpha (transparency) of a layer mask another layer in friction. After effect equivalent (track matte) : https://www.youtube.com/watch?v=zgbXGqYMxq4

• setup two layers, one mask (above) and one to be masked (below) group them together
• set the mask (above) blend mode (math operation between this layer and below) to DstIn to have it "cut" through the entire composition using alpha channel to limit the effect to the layer(s) in the group only, promote the group to layer, so the blend modes would not be retain outside of this group, interacting with the rest of the composition.

Do you know friction ? It is an awesome open source 2d animation software, early stage, which could replace after effect

Unofficial discord https://discord.gg/FkjnM2r2JD Official page https://friction.graphics/