Hi,
If you want the proxy server settings to be applied to users depending on the IP subnet in which they work, you can use the GPP Item Level-Targeting.
To do this, switch to the Common tab in the policy settings and check the Item-Level Targeting option.
Click on the Targeting button.
Select New Item > IP address ranges.
Specify the range of IP addresses in your subnet for which you want to apply proxy settings.
Select New Item > IP address ranges. Specify the range of IP addresses in your subnet for which you want to apply proxy settings.
For more information , you can refer to:
https://theitbros.com/config-internet-explorer-11-proxy-settings-gpo/(Third-party link)
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If i misunderstand you ,please feel free to let me know.
Best Regards,