With the release of the new version of Capture One in May 2020 (13.1.0), came some new features that meant some old dependencies in the software had to be removed.
Unfortunately, with this update, a few Macintosh computers are now incompatible with Capture One 20 (13.1.0) and later versions. The processors (CPUs) in these older machines are no longer supported due to the lack of SSE4.2 support - something Capture One relies on in order to work efficiently.
Put simply, if your Mac was manufactured around 2010 (or older) then it is likely that it will not be able to run Capture One 20 (13.1.x), so you will have to use version Capture One 20 (13.0.4) that can be downloaded here.
The earliest supported processor is the Intel i3 (1st generation).
This is part of the constant developmental nature of Capture One, as we continue to utilise the newest hardware and software possible, in order to give you a smooth editing experience.