Steps to reproduce:

1. Ask for the key to the agents

The tests were done in the training 6.0 machines, the traditional in podman and the aget2 in the SO provided.

bash-4.4$ zabbix_agentd -t proc.get
proc.get                                      [m|ZBX_NOTSUPPORTED] [Unsupported item key.]
bash-4.4$ zabbix_agentd --version
zabbix_agentd (daemon) (Zabbix) 6.0.6
Revision 3f7597e 27 June 2022, compilation time: Jul  5 2022 12:51:42

Copyright (C) 2022 Zabbix SIA
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it according to
the license. There is NO WARRANTY, to the extent permitted by law.

This product includes software developed by the OpenSSL Project
for use in the OpenSSL Toolkit (http://www.openssl.org/).

Compiled with OpenSSL 1.1.1k  FIPS 25 Mar 2021
Running with OpenSSL 1.1.1k  FIPS 25 Mar 2021

[root@trainer ~]# zabbix_agent2 -t proc.get
proc.get                                      [m|ZBX_NOTSUPPORTED] [Unknown metric proc.get]
[root@trainer ~]# zabbix_agent2 --version
zabbix_agent2 (Zabbix) 6.0.6
Revision 3f7597e3ea3 27 June 2022, compilation time: Jun 27 2022 14:25:51
Plugin support version 1.0

Copyright (C) 2022 Zabbix SIA
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it according to
the license. There is NO WARRANTY, to the extent permitted by law.

This product includes software developed by the OpenSSL Project
for use in the OpenSSL Toolkit (http://www.openssl.org/).

Compiled with OpenSSL 1.1.1g FIPS  21 Apr 2020
Running with OpenSSL 1.1.1g FIPS  21 Apr 2020

We use the library Eclipse Paho (eclipse/paho.mqtt.golang), which is
distributed under the terms of the Eclipse Distribution License 1.0 (The 3-Clause BSD License)
available at https://www.eclipse.org/org/documents/edl-v10.php

We use the library go-modbus (goburrow/modbus), which is
distributed under the terms of the 3-Clause BSD License
available at https://github.com/goburrow/modbus/blob/master/LICENSE

Documentation

https://www.zabbix.com/documentation/6.2/en/manual/config/items/itemtypes/zabbix_agent?hl=proc.get