FRD "needs earlier Java version" - Mac OS (Catalina) refuses!

Hello!

I am trying to install the latest FRD on my Mac's Catalina v.10.15.5. FRD says it needs to install eariler Java SE 6, so I download it and try to install - Mac OS refuses to install earlier Java saying "can't install on your hard disk since the newer Java version is already installed" - deadlock)

The installed Java version reports the following:

java version "1.8.0_251"
Java(TM) SE Runtime Environment (build 1.8.0_251-b08)
Java HotSpot(TM) 64-Bit Server VM (build 25.251-b08, mixed mode)

Follow this tutorial to make a modified package for Java:
Modified Script to install Java SE 6 (Java ForOS)

What's the latest Mac OS this is compatible with?
I try to run this on macOS 11 (Big Sur), with a new install of Java 9. But I just get the error

Fatal error.
This is unexpected error, which can lead to application instability.
An application restart may help.
Please report this error to the authors.

and I can't expand the "details" because it keeps glitching or something.

I got the same error when I was on Java 8.

FRD 0.9u4 runs fine on my other Mac running High Sierra so I am assuming you can't go newer than that OS?