ERESOLVE issues with npm@7 are common because npm 7.x is more strict about certain things than npm 6.x. Often, the easiest resolution is to pass the --legacy-peer-deps flag to npm (e.g., npm i --legacy-peer-deps) or else use npm@6.
If that doesn't work immediately, perhaps try removing node_modules and package-lock.json first. They will be recreated.
(Tip: You don't need to uninstall npm@7 to use npm@6. Use npx to specify the version of npm instead. For example: npx -p npm@6 npm i --legacy-peer-deps.)