ClassicPress has less of an admin tax than WordPress…the way WordPress used to be. An administration tax is the time you spend administering a site over actually creating content for it. WordPress and ClassicPress both have some of this…but as WordPress moves farther and farther away from its roots, you end up having to update things to work well with the latest. This means that while right now, most WordPress plugins work with ClassicPress…that might increasingly not be the case….at least not without a small amount of work.
For my own plugins, I intend to test them against both systems for the foreseeable future. But as WordPress drifts further away from its roots, and therefore from ClassicPress, people writing plugins that can work without the block editor dependencies becomes increasingly important.
If you already have a WordPress Site, you can install the ClassicPress migration plugin. You can install ClassicPress by following the other options here.