Copying the shell instructions for the plugin via Craft Control panel > Plugin Store and attempting to install via the console results in an error "requirements cannot be resolved to an installable set of packages"
Root composer.json requires nystudio107/craft-emptycoalesce ^1.0 -> satisfiable by nystudio107/craft-emptycoalesce[1.0.0, ..., 1.0.6]
nystudio107/craft-emptycoalesce[1.0.0, ..., 1.0.6] require craftcms/cms ^3.0.0 -> found craftcms/cms[3.0.0, ..., 3.7.42] but it conflicts with your root composer.json require (4.0.2).