I was recently given an old 2010 21.5 iMac. I was able to install MacOS 10.15 on it. Whenever I attempt to download pages, numbers, keynote or other Apple software it tells me that I need to have MacOS 11.0 installed. I can't install MacOS 11 on this machine and I do not have a purchase history of those apps to download them. How can I download compatible apps for my iMac?