Attribute Filter for local domain in AzureADConnect

That's really up to you. The .local value can be present in multiple attributes, so you need to decide which one to filter on. A simple solution is to populate one of the custom/extensionattributes for the users you want to filter and configure a rule as shown here: https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnectsync-configure-filtering#configure-attribute-based-filtering

Or you can create a more complex rule that directly checks the value of say the proxyaddresses attribute, following the instructions here: https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnectsync-change-the-configuration