I have seen this error, and it can be no more than a problem with connecting to the server, in which case it disappears if you wait for a time before trying again. The more serious issue is that neither Microsoft nor Apple support Windows 11 using Boot Camp, as Intel Macs lack the necessary Secure Boot, Trusted Platform Module (TPM) Security Processor, and Core Isolation. There are ways of disabling security protection (even Microsoft Support suggest a link to advice for installing on 'Incompatible Devices') but, from experience, although they work for a time, I cannot recommend them. For one Intel Mac, when Bootcamp Windows 11 stopped updating, I fled to Parallels, the other Intel Mac I left on Windows 10. The advice about removing external drives is a logical Boot Camp Assistant alert (and the use of a bootable USB drive can help), but it also occurs with some Windows updates like 24H2, as seen last month in a silicon Mac virtual environment.