This extension loads the ProseMirror Gapcursor plugin by Marijn Haverbeke, which adds a gap for the cursor in places that don’t allow regular selection. For example, after a table at the end of a document.
Note that Tiptap is headless, but the gapcursor needs CSS for its appearance. The default CSS is loaded through the Editor class.
npm install @tiptap/extension-gapcursor
Are you using Yarn, pNPM, npm 6 or less?
Unfortunately your package manager does not install peer dependencies automatically and you have to install them by your own. Please see here which packages are needed and how to install them.