well you don't put a virus in winrar.
The problem is that ini files can be a security issue. For example, desktop.ini (which collect all information about icons and folder name so that file explorer shows them to you) can be tampered so that a virus.exe would be shown as firefox.exe on your computer (name changed and icon changed)
ini alone aren't a problem, but an ini in a rar file with an virus.exe may be (if somehow it manage to override your desktop.ini which is another story)
But sometimes, windows defender can be a little too trigger-happy with ini files, and display that error code which means that someone can take full control of your computer. Which can be true (as seen in the example), but very unlikely in this scenario. It has to be chained with others vulnerability or some extrem user dumbness.