value class MyClass(val myParam: BigDecimal? = null) is flagged with “A parsing error occurred in this file” at this precise line
inline classes (value class) have been added to Kotlin in version 1.4.30 which was released on February 3rd 2021 (What's new in Kotlin 1.4.30 | Kotlin)
There seems to be no update available for the Kotlin plugin
Your version is past EOL and Kotlin analysis has come a long way since then. You should upgrade to either the latest version or the current LTS at your earliest convenience. Your upgrade path is: