I have purchased Capture One 12 with a bundle of Styles. Will I be able to use them in Capture One 20 (and later versions) or do I have to purchase them again?
Once you purchased Styles either separately or together with perpetual license or subscription, you can use them onwards even after an upgrade or switching to another license. For instance, in case you purchased Capture One 12 Pro with a bundle of Styles and have recently upgraded to Capture One 21, you can simply use those Styles in the latest version of the software, so you do not have to purchase those once again.
It is always possible to retrieve the Style packs you have once purchased from your FastSpring account at https://captureone.onfastspring.com/account/
NOTE: Beyond Styles can be used only in Capture One 20 and later versions.