I've tried using the new existential syntax in Xcode Playground in Xcode 14 beta 3 and it seems like Xcode is using the wrong version when compiling the playground.
The exact same code (same file) compiles and runs fine with xcrun swift but in the playground window I get several errors that make me suspect that it doesn't use the latest Swift compiler:
expression failed to parse:
error: 20220710_173924.playground:16:29: error: type 'any Costume' cannot conform to 'Costume'
costumes.first(where: { hasBells($0) })
^
20220710_173924.playground:16:29: note: only concrete types such as structs, enums and classes can conform to protocols
costumes.first(where: { hasBells($0) })
^
20220710_173924.playground:11:6: note: required by global function 'hasBells' where 'some Costume' = 'any Costume'
func hasBells(_ costume: some Costume) -> Bool {
^