Zoho CRM's original Gmail integration, the Contextual Gadget, was built on a Google technology that Google has since deprecated. It has been superseded by newer, actively maintained options.
Between them, current Gmail integrations for Zoho CRM cover creating Leads and Contacts from an email, viewing a customer's deal size, deal stage, and pipeline position without switching tabs, adding notes against a record, viewing related Campaigns and Deals, and, on the Chrome extension, converting a Lead to a Contact directly from your inbox.
Search for "Zoho CRM for Gmail & Inbox" in the Chrome Web Store for the extension, or "Zoho CRM for Gmail" in Google Workspace Marketplace for the add-on. Both are free. After installing, you'll sign in to your Google account and then authenticate your Zoho CRM account before the integration becomes active.