Pop OS does not have a minimize and maximize button because it has gone for a keyboard shortcut approach instead. You can press the keyboard shortcut Super + M to maximize a window and Super + H to minimize a window. The "Super" key is the key on your keyboard that has the operating system logo on it. In most cases, you are probably using a keyboard that was made for Windows, so that would be the Windows Key.

All of the Pop OS keyboard shortcuts can be found on their website.

Although I'm not sure if it still works, as of 2017 you could install the gnome-tweak-tool and enable the minimize and maximize buttons from the Windows options.

Hope this helps.

hello

shlomo_bachar....................

Could it be that you're in Tablet Mode instead of Desktop Mode ?

You can check Windows Settings to make sure ...... 

and if you are in Tablet Mode, change the setting to Desktop Mode.

Then those minimize and maximize buttons should be back

thank you!