This is a long running official thread that still sees a lot of activity. Josh Peterson of Unity remains active in the thread, updating people about plans for future versions of Unity using Core CLR so that they can more directly support newer C# features as they are released. But, there may be newer things that you just cannot use yet until Unity supports them.
“EDIT (October 27, 2023): We’re focused internally on developing and shipping new .NET support, with our current target being .NET 8. We don’t have a shipment date to share publicly yet, but I’ll respond on this forum thread with details when I do.”