It looks like you may be attempting to use string interpolation (https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/tokens/interpolated), but you don't have the formatting quite right. There are a few ways you can go about solving this, but the following is the closest to what you're doing.
I'm not sure what all your SideBarMenuItem component does, but I'm guessing this is what you're looking for:
...
<SideBarMenu Icon="far fa-circle" Link="@($"/rapportiselezione/{id}">
...Then you'd need to assign a value to the id property in your code block. Just for example sake, I'll simply set it manually, but you'll be setting it in a method somewhere.
@code {
int id = 1;
// Then the rest of your code, methods, etc.
...
}Of course, the rapportiselezione page will need to have a page directive at top for your route that's like:
@page "/rapportiselezione/{Id:int}"and in your code block of that page you'll need a public parameter to get the Id.
@code {
[Parameter] public int Id { get; set; }
...
}