This is the "reboot announcement". Starting with .NET 5 there's only one .NET again that matters (though you'll hear lots of legacy support complaints for years

This is the "reboot announcement". Starting with .NET 5 there's only one .NET again that matters (though you'll hear lots of legacy support complaints for years to come). 5 is now the highest version number and the next version number is 6 like you would expect. There's no other versions you need to know unless you have to support legacy code (and there, it's probably time to reboot if you are supporting certain types of legacy code).