mBlock block’s codes are run in a sandboxed environment (on a “VM”, or Virtual Machine in the browser), so block’s functionality is limited. Otherwise, people could easily make malicious extensions that interacted with mBlock’s data or your account data in potentially harmful ways.
See
https://builtin.com/software-engineering-perspectives/sandbox-environment
and
https://www.proofpoint.com/us/threat-reference/sandbox
So to answer your question, some scripts cannot execute without mBlock’s permission (you could try to contact mBlock and have them make an exception for you).