https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.builder.sparouteextensions.mapspafallbackroute?view=aspnetcore-3.1&viewFallbackFrom=aspnetcore-6.0
SpaRouteExtensions.MapSpaFallbackRoute Method (Microsoft.AspNetCore.Builder) | Microsoft Learn
Configures a route that is automatically bypassed if the requested URL appears to be for a static file (e.g., if it has a filename extension).
methodmicrosoftaspnetcorebuilderlearn