Dec 16 2020
This flag that was just added today to Edge Version 89.0.736.0 (Official build) canary (64-bit)
can disable Alt + Tab experience
the description says:
"Allows Windows to show open Microsoft Edge tabs in OS experiences like Alt + Tab, pinned sites, and more. – Windows"
so regardless of what your settings are in Windows
you can stop Edge tabs to appear as separate windows in Alt + Tab view.