I think the best solution would be to build Audacity 2.4.2 from the source code. If cmake version 3.15 or later is available from your package manager, then building Audacity is quite straightforward - I’ve written step by step instructions for Ubuntu 20.04 which I think should be the same on Linux Mint 20.
I think Mint 20 should have cmake 3.16, which will be perfect - perhaps you could check if that is the version in your package manager.
If you do decide to try building from source, completely remove all package versions of Audacity before you start.