Startup boost is available on Windows devices (excluding Windows 10X and servers) with more than 4GB of RAM, or more than 1GB of RAM if the device has a modern disk (modern HDD with Trim and Seek Penalty or SSD), when Microsoft Edge is used every few days without any conflicting extensions installed. These criteria were informed by experimentation data.
support.microsoft.com/en-us/topic/get-help-with-startup-boost-ebef73ed-5c72-462f-8726-512782c5e442
See also other microsoft-edge-startup-boost-tagged articles.