Installing Java 6 on macOS Catalina

Download at Apple
Open Script Editor and enter the following

set theDMG to choose file with prompt "Please select javaforosx.dmg:" of type {"dmg"}
do shell script "hdiutil mount " & quoted form of POSIX path of theDMG
do shell script "pkgutil --expand /Volumes/Java\\ for\\ macOS\\ 2017-001/JavaForOSX.pkg ~/tmp"
do shell script "hdiutil unmount /Volumes/Java\\ for\\ macOS\\ 2017-001/"
do shell script "sed -i '' 's/return false/return true/g' ~/tmp/Distribution"
do shell script "pkgutil --flatten ~/tmp ~/Desktop/ModifiedJava6Install.pkg"
do shell script "rm -rf ~/tmp"
display dialog "Modified ModifiedJava6Install.pkg saved on desktop" buttons {"Ok"}

Compile and Run (hammer and playback items, respectively)
Select the JavaForOSX.dmg
The modified .pkg for Catalina will be placed on the Desktop.

Sources

https://www.harrisgeospatial.com/Support/Self-Help-Tools/Help-Articles/Help-Articles-Detail/ArtMID/10220/ArticleID/23780/Mac-OS-Catalina-1015-ENVIIDL-and-Legacy-Java-6-Dependencies