You are using Acronis True Image 2020 or later on Windows 7.
It is not possible to activate Acronis Active Protection: the option is grayed out. No error message appears.
Windows update KB2533623 is required for Active Protection on Windows 7.
Download and install Windows Update KB4457144 from Microsoft Update Catalog (this update supersedes update KB2533623). Select the appropriate download for your system.
Instead of downloading a single update, you can also install all available Windows Updates for your system: see How to download a Windows update manually