How to reinstall high sierra

I need to reinstall high sierra on macbook pro after upgrade to catalina. I have downloaded the relevant os install from app store but they will not run on my computer with error message saying the installer is too old to run on my computer.

there are lots of threads on google suggesting that apple purposely broke the installation software to stop people reinstalling older os.

is there anywhere or way I can obtain a official working copy of high sierra installer?