Now Apple has stopped charging for the ageing operating system versions.
Prior to June 2021 OS X 10.7 Lion or Mountain Lion would have cost you £19.99 each for the download code. Until recently if you wanted to upgrade (or downgrade) old Mac to Mac OS X Lion (from 2011) or Mountain Lion (from 2012) you needed to pay Apple and the company would send you a special download code to use on the Mac App Store.