If you try booting into Big Sur in Remote (Internet) Recovery, you’ll get Catalina instead. But nowhere does Apple alert users to this problem.
OCSP
Why does it take 2 years to realise that macOS has been checking signing certificate validity online?
Although most were worried about Apple’s failure to deliver upgrades to Big Sur, the most serious problem left many users unable to launch any apps.
The Eclectic Light Company 