I agree that the article is nonsense, but more importantly, we haven’t used Mono in many years.
“.NET Framework” and “.NET Core” are both obsolete things.
Since 2020, all reasonable releases of this thing are an open source project called “.NET”.
.NET Framework died at 4.x over a decade ago. It’s still around, but only gets security updates. While it is included with Windows, it is recommended by Microsoft that no one use it,
.NET Core was the new thing and restarted the versioning at 1.0. It died with 3.1, when “.NET 5” was introduced in 2020.
Since then, there has been a unified project under this open source '.NET" branding: .NET 6, 7, 8, and recently, .NET 9. If anyone is using .NET in modern times, they are using this.