Adding a custom font as PrivateFont in the appssettings.json is not respected.
When the font is installed, it works also for the report in the viewer.

The issue may be reproduced with the Reporting WinUI example for .NET 6.

The Stack Trace states:
CSharp.Net6.WinUIIntegrationDemo Warning: 0 : A font family for font "MICR" cannot be found. Exception: Font 'MICR' cannot be found. Font 'MICR' is substituted with font 'Microsoft Sans Serif'.