New Microsoft Edge to replace Microsoft Edge Legacy with April’s Windows 10 Update Tuesday release
This is an Known issues in this update:
Devices with Windows installations created from custom offline media or custom ISO image might have Microsoft Edge Legacy removed by this update, but not automatically replaced by the new Microsoft Edge. This issue is only encountered when custom offline media or ISO images are created by slipstreaming this update into the image without having first installed the standalone servicing stack update (SSU) released March 29, 2021 or later.
If you have already encountered this issue by installing the OS using affected custom media, you can mitigate it by directly installing the new Microsoft Edge.
You could refer to the following official article as your reference:
Hope above information can help you.
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