Logic Pro on Catalina OS

Hi guys, my IMac Pro is only about 6 years old but won’t upgrade the OS software any further than Catalina.

I really want to start using Logic Pro but I won’t download as needs to be OS 11.0 or higher. I really don’t want the expense of buying a new machine. Is there somewhere I can buy an earlier version of Logic which will be compatible with Catalina OS?

Ive searched the web but just can’t see any info.

Thanks

Nick