I had a user in chat recently who was trying to install Jetpack so they could enable WooCommerce Services. They kept getting an error message saying:
Installation failed: Destination folder already exists.
At some point the site had Jetpack, but it had been partially removed and was now blocking WordPress from installing it again.
They had already been told to use FTP and remove the jetpack folder from
/wp-content/plugins/ but they were not able to locate their FTP credentials. They also had run into trouble getting help from their host.
But there is another quick workaround for this, the Update Theme and Plugins from ZIP File plugin. Back in ancient times, the only way to update a theme or plugin was to open up an FTP program and upload the new version to your server directly.
Plugins like this one made it easier to update since you could upload a ZIP file through WordPress instead of using FTP. Modern update systems have rendered these obsolete, but they can help out our user since they allow installing into existing folders.
I asked the user to install the plugin and then try installing Jetpack by uploading the ZIP file. Just like that, it installed.
So now if you ever run into an issue with a plugin not installing because the folder already exists, you’ll have another tool to fix this that doesn’t require FTP access.