Invert a mask to flip what’s visible — it’s handy when you want to hide the center and keep everything else showing.
Steps to invert a mask
Select your masked layer and press MM to open all mask properties.

Find Inverted next to your Mask and check the box — the hidden and visible areas swap instantly.

Tweak Mask Feather and Mask Expansion if the edge looks too sharp or too tight for what you need.

One more thing
If you have multiple masks, you can invert only the one you need — each mask has its own Inverted toggle, so they work independently.
Related how-tos
How to draw masks in After Effects
How to feather a mask in After Effects
How to use mask expansion in After Effects
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