The .NET ecosystem is giving me a lot of confidence these days. I've been on this rollercoaster since .NET Core 2.x and don't think I will be getting off any time soon. We recently upgraded from 3.1 to 6, which was a total non-event. The code base that was around for Core 2.x is still the same one we have today. Some substantial changes made to the web interfaces and hosting, but nothing in the business logic or data…
If you continue to use .NET Framework 4.8, your software will receive security updates until the heat death of the universe, too much, including Windows itself, depends on it. (Same, hilariously, with Visual Basic 6.) Microsoft's lifecycle for new runtimes is so short you're better off using a dead one.
.NET Core has too many caveats and too few selling points to get any reasonably competent desktop developers to move over, IMHO, especially considering the fact that every executable you ship to customers has a Microsoft imposed support death date.