I've been developing Eclipse apps for...a long time. And only now discovered this.
When starting Eclipse on Windows you may see the "Initializing Java Tooling" progress message and have to wait a long time for Eclipse to start.
This is caused by Windows Defender scanning all *.jar files when Eclipse starts.
So you can add the Eclipse folder, workspace folder, and any project folders to the Windows Defender exclusion list.
Now my Eclipse starts instantly!
Of course, it goes without saying that excluding files and folders from anti-virus checks is a risk and should not be done unless you know what you are doing.