[StructLayout(LayoutKind.Sequential)]
public unsafe struct Font
{
    public int BaseSize;
    public int GlyphCount;
    public int GlyphPadding;
    public Texture Texture;
    public Rectangle* Recs;
    public GlyphInfo* Glyphs;
}

[StructLayout(LayoutKind.Sequential)]
public unsafe struct Font
{
    public int BaseSize;
    public int GlyphCount;
    public int GlyphPadding;
    public Texture Texture;
    public Rectangle* Recs;
    public GlyphInfo* Glyphs;
}

[StructLayout(LayoutKind.Sequential)]
public unsafe struct Font
{
    public int BaseSize;
    public int GlyphCount;
    public int GlyphPadding;
    public Texture Texture;
    // Already tried [MarshalAs(UnmanagedType.ByValArray)]
    public Rectangle[] Recs;
    public GlyphInfo[] Glyphs;
}

[StructLayout(LayoutKind.Sequential)]
public unsafe struct Font
{
    public int BaseSize;
    public int GlyphCount;
    public int GlyphPadding;
    public Texture Texture;
    // Already tried [MarshalAs(UnmanagedType.ByValArray)]
    public Rectangle[] Recs;
    public GlyphInfo[] Glyphs;
}

Error SYSLIB1051 : The type 'MyNamespace.Font' is not supported by source-generated P/Invokes. The generated source will not handle marshalling of parameter 'font'.

Error SYSLIB1051 : The type 'MyNamespace.Font' is not supported by source-generated P/Invokes. The generated source will not handle marshalling of parameter 'font'.