I've already found the actual problem (ARC not calling the destructor), see <https://github.com/nim-lang/Nim/issues/19794> . As a workaround you can change nim-decimal yourself so it uses an object and defines a destructor on it.
- Memory Leak with --gc:orc and Nimble Decimal Library rbohl64
- Memory Leak with --gc:orc and Nimble Decimal Library Yardanico
- Memory Leak with --gc:orc and Nimble Decimal Library rbohl64
- Memory Leak with --gc:orc and Nimble Decimal Librar... Yardanico
