Comment by ygra

AFAIK you can still use it for older frameworks. The compiler embeds the attributes into the assembly when they're known to not be part of the runtime library [−3.7]. You can do the same with the various conditional nullability attributes.

[−3.7]: https://sharplab.io/#v2:EYLgHgbALAPgAgZgARwExIMJIN4FgBQSRKyc...