It depends on your definition of “safe”.
Let’s suppose that you really like to buy clothes on ebay while having your lunch.
While in incognito, your browser by default will not save on disk any cookies, history, or temporary cached items. A technician with access to your PC will not be able to tell today what you browsed yesterday.
However, if someone has access to routers you use and control over your network, things are different. An IT person with control over your network will be able to tell that yesterday you used ebay for an hour and a half, but they don’t know what you were looking for.
Then there is the matter of browser plugins.
In an enterprise environment, IT can and will manage your browser, including enabling certain browser extensions in incognito mode.