First, check if you are subject to the 2 years ban – this is written on your visa stamp and in the DS2019 form. If both of them say you are, then you have to get the waiver before you apply for the adjustment of status and work authorization. At the same time, you may file I-140 without the waiver. If you are not subject to the ban, then you don’t need the waiver at all. If the visa stamp and DS2019 state two different things, then you have to request the so-called Advisory Opinion to figure out if you are subject to 2 years ban.