Cannot assign policy for usernames that have a backslash by using MACP (KB5018063)

Symptoms 

In the Modern Admin Control Panel (MACP) of Microsoft Skype for Business Server 2019, you can't assign or change policies for usernames if any username contains a backslash (\) character.

Resolution 

To fix this issue, install the following updates for Microsoft Skype for Business Server 2019: 

• October 2022 cumulative update 7.0.2046.409 for Skype for Business Server 2019, Core Components

• October 2022 cumulative update 7.0.2046.409 for Skype for Business Server 2019, Macp Web Components