In the current situation it's not possible to distinguish if you've installed zabbix agent or agent2 onto a Windows or Linux OS. You could have several Linux/Windows server, and they all run a zabbix agent version 5.2.6, but it would be impossible (with official item keys) to spot the difference between generations.
Let's say you want to switch ALL your Zabbix agents(1) on 5000+ hosts. How do you know you've missed one?
Therefore I suggest to create a new item key, like for example: agent.generation or agent.type or agent.gen that returns a "1" or "2".
Additionally, if this request gets addressed I propose that this change should include adjustments to the official zabbix agent template to include the new method of differentiation between generation 1 and 2: https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/templates/module/zabbix_agent