Why doesn’t my example satisfy this “requires” expression?

Here is a full example. However, your concept is correct. There was a change in C++20 that allowed capturing lambdas in unevaluated context. See this answer for more details on that. If you update your compiler your concept should be valid. The latest VS preview (16.11) supports this change (although intellisense shows it still as error).

https://stackoverflow.com/questions/68031646/why-doesnt-my-example-satisfy-this-requires-expression