This is a discussion on Win 10 shrink icon within the Windows 10 Support forums, part of the Tech Support Forum category. (or whatever the box between the x and the solid line is called in the upper right column).
Post a screenshot of the window for which the maximise/restore button doesn't work. If you need help with how to post a screenshot, open the link in my signature for a tutorial explaining various ways you can do it.
At full screen the middle button will be 2 pages or boxes one behind the other, as pictured.
If you click it, it should turn to 1 Box. If so, you then can grab a corner of the window by placing your pointer there and it should turn into a double sided arrow and you can shrink the window to your desired size by dragging it inward.
If when you click the double boxes it doesn't change, then you may need to reinstall your browser.
Thanks. Yes that has always worked with windows, but now it doesn't. Even trying to resize the window "manually" with the cursor on the edges, as you suggested doesn't work. Weird.
I can't imagine how to reload Windows: it's not the browser: the same thing happens with other browsers and any app, like Word.
Your screen resolution seems pretty low. Is that how you like it? It looks like 1024 x 768, which is the minimum supported by many modern programs. Change it to the native resolution of your display. For your thinkpad, it's most likely 1366 x 768, or higher, but not lower than that.