Yesterday, 10up officially announced Convert to Blocks, a WordPress plugin for transforming classic posts into blocks. The goal is to provide users with a safe migration route for old content while removing the burdens of other options in the space.
I briefly mentioned this plugin in an article covering bulk conversion in the Ask the Bartender series. However, I could not recommend it to most users because it was hosted on GitHub, a site that is geared toward developers. With it now officially in the WordPress plugin directory, it is a much more user-friendly option.