We struggled with this for quite a while too. Google discusses an option about using registry values for this in this article:

https://chromeenterprise.google/policies/#LocalNetworkAccessAllowedForUrls

What we ended up doing was creating this registry path:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome\LocalNetworkAccessAllowedForUrls

And then adding a new string value, named 1 with a value of the test domain we worked with, e.g. [*.]our.test.domain.com

This then appeared to have applied the Local Access Network" exemption to all the web apps we test under that domain.