Mapping (spelt "Select" quite often in LINQ) is entirely normal and promoted going forwards. It can optimize extremely well for simple cases. By default it is not parallel and compiles to an underlying for loop.
Or you can use it with Tasks. https://itnext.io/fun-csharp-doing-linq-to-tasks-because-tas...
(caution: contains the M word)
More from Microsoft: https://devblogs.microsoft.com/pfxteam/tasks-monads-and-linq... ; referencing Lippert https://ericlippert.com/category/monads/
ContinueWith is not a broken "map". What people usually want is Select. https://learn.microsoft.com/en-us/dotnet/csharp/linq/standar...
Does LINQ's map come with a plethora of problems like I'm told Task's map does above?
Should you avoid mapping because 'it's the old callback model' which doesn't belong in modern code?
Is map fit for purpose, or has it been disavowed?