Secure Boot

When done correctly, "Secure Boot" is designed to protect against malware by preventing computers from loading unauthorized binary programs when booting. In practice, this means that computers implementing it won't boot unauthorized operating systems – including initially authorized systems that have been modified without being re-approved.

– Stand up for your freedom to install free software — Free Software Foundation…

FSF calls it [[Restricted Boot]]:

This could be a feature deserving of the name, as long as the user is able to authorize the programs she wants to use, so she can run free software written and modified by herself or people she trusts. However, we are concerned that Microsoft and hardware manufacturers will implement these boot restrictions in a way that will prevent users from booting anything other than Windows. In this case, we are better off calling the technology Restricted Boot, since such a requirement would be a disastrous restriction on computer users and not a security feature at all.

– Stand up for your freedom to install free software — Free Software Foundation…

Secure Boot support is required for Windows 11 installation.