See -ZBX-15217- (and the discussion in -ZBX-9435- for historical reference).

As mentioned, the new compressed version of the Zabbix Protocol has not yet been documented in the protocols pages at https://www.zabbix.com/documentation/current/manual/appendix/protocols/server_proxy

Also, https://zabbix.org/wiki/Docs/protocols#Zabbix_4.0 should at least mention the switch to compression as well.

Please make sure these changes are documented as they might be referenced by (security) vendors (as mentioned in -ZBX-15217-).