I have purchased a number of style packs to use in Capture One 11 and 12. Will those simply work in Capture One 20? Can I use those in older versions of the software as well?
After you have purchased and downloaded style packs, you need to import those into Capture One.
As the function to import styles appeared in Capture One 10, you can install those style packs in Capture One 10, Capture One 11, Capture One 12.
Consider that you will be also able to install style packs in Capture One 20 when it is available.