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!
See:
https://www.windowscentral.com/how-exclude-files-and-folders-windows-defender-antivirus-scans
https://bugs.eclipse.org/bugs/show_bug.cgi?id=548443
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.