You are unable to install the Symantec Endpoint Security (SES) agent, and it says it's unable to reach the cloud resources. You've already whitelisted the sites listed in URLs that allow SEP and SES to connect to Symantec servers (broadcom.com). Tests in Symantec Download Manager unable to reach cloud resources (broadcom.com) pass as well.
FSD (SES installation) logs may show a message like the following:
2021-09-28-14-59-37-383 : 0x0B6C : Error : Unable to connect https://usea1.r3.securitycloud.symantec.com/r3_epmp_i/status, hr 0x80072F8F
Revocation check or root download failure.
In addition to the URLs listed in the links above, please ensure that public SSL/TLS certificates can be validated with the CRL per: SSL/TLS OCSP and CRL in DigiCert new Web PKI hierarchy certificates. It may also be necessary to ensure that root updates have not been disabled by GPO, and that access to ctldl.windowsupdate.com is allowed.