Simulacrum VS Shapeless

The Cats ecosystem offers mature named abstractions providing algebraic laws virtually identical to those offered by Haskell and PureScript and that have stood the test of time, at the cost of relying on a "design pattern" approach to implementation you have to squint a bit to see ("typeclasses" based on higher-kinded types and implicit arguments) and that sometimes doesn't play nicely with Scala's colored local type inference. The selling point of this, coupled with parametricity ("tagless-final style"), is the ability to reason algebraically about your code.

Scala 2-only: * Shapeless (there is Shapeless for Scala 3 but less often needed as basic things are in Scala 3)

This is the FromMap typeclass in Shapeless. Note that there’s a companion syntax package for it providing .toRecord for any Map and an appropriately-structured Record (and a Record is the LabelledGeneric representation of a case class).

If that's what you want, you can use Shapeless' records and HList. You can probably replicate this in plain Scala 3 with tuples and literal types as you said. It won't play nice with your others libs though but maybe there are integrations.

See the Shapeless Sized example.

Shapeless has Sized: https://github.com/milessabin/shapeless/blob/v2.3.9/core/src/main/scala/shapeless/sized.scala

I know that libraries like Scodec and shapeless were rewritten practically from scratch for Scala 3, taking advantage of the next syntax and internals, as well as protoquill - a Scala 3 implementation of Quill.

please show me something like this: https://akka.io/ or this: https://zio.dev/ or this: https://github.com/milessabin/shapeless

That largely depends on the type system. Languages like Haskell and Scala which have much more powerful type systems than C/Java/Go/etc absolutely do allow you to do those sorts of things. It is a bit harder to wrap your head around to be sure and there are some rough edges, but once you get the hang of it you can get the benefits of static typing with the flexibility of dynamic typing. See https://github.com/milessabin/shapeless or a project that I've been working on a lot lately https://github.com/zio/zio-schema.

Just use cats and use the apply syntax .mapN for this. Seriously. There isn't a way to do it without generating source code that I can see in the api. Scala 3's HList Tuples aren't like Shapeless 2's HLists and I can't figure out a way in the api to reduce the tuple members down from (A, B, C, D) into an E, generically, yet with Scala 3 poly functions, unlike what you could do in Shapeless 2 with HList

Scala has sparked a huge ecosystem of very high quality libraries (Cats, Scalaz, shapeless, to name but a few). I think a major reason for this is that Scala attracts developers who value the advantages of the JVM, but are fed up with the limitations of the Java programming language and understand the benefits of an expressive type system and functional programming.