got this error today while working on a project with IONC after sending the ionic start command and selecting react with reference options.
npm WARN deprecated [email protected]: core-js@<3 is no longer maintained and not recommended for usage due to the number of issues. Please, upgrade your dependencies to the actual version of core-js@3.
to get it fixed i tried these commands in linux ubuntu
npm cache clean --force
sudo npm install -g @ionic/cli