The Powerscripts Installer uses a program provided by Adobe called ExManCmd to install Powerscripts. ExManCmd is updated with every new release and is required to install PowerScripts to the latest version of Illustrator. Once powerscripts is installed on a computer it will be available to ALL version of illustrators
ExManCmd version 7.11 which is required to install to Illustrator 2021 has a bug, so that on some systems it will not run and returns no errors, It simply fails to execute any commands.
There is currently no update from Adobe to fix this issue
The most recent version of PowerScripts Updater V2.3.5 available from www.o2creative.co.nz/installer has the current version of ExManCmd 7.11 and also includes an older version. The older version of ExManCmd will only detect Illustrator 2020 or earlier, so to install PowerScripts for Illustrator 2021 you will need to temporally install Illustrator 2020 then run the older installer, this will detect Illustrator 2020 and install PowerScripts, then once installed PowerScripts will work on Illustrator 2021 and you can safely remove the older version of Illustrator.
Installation Steps: