The basic principle behind tracking Google Sheet opens is the same as the one behind email tracking with a transparent pixel. In a Google Sheet, we will use the IMAGE()function, which will call a deployed Google Apps Script web app URL with some parameters in the query string. The web app will be able to do whatever you need among the following: record to a spreadsheet, create a message via a messenger, or simply send an email.
Source: Tracking Google Sheet Opens with Google Apps Script
Member of Google Developers Experts Program for Google Workspace (Google Apps Script) and interested in supporting Google Workspace Devs.