Can I apply for the I-601A waiver if I am filing an I-485 Application for Adjustment of Status?

No. A foreign national who is in the US and is eligible to apply for an I-485 Application for Adjustment of Status would not apply for an I-601A waiver. If they require a waiver of the 212(a)(9)(B) Unlawful Presence bar, they would file an I-601 waiver application. The I-601A Provisional Waiver application is only for those who are currently in the US, but will be required to apply for an immigrant visa at the consular post abroad because they are not eligible to apply for an I-485 Application for Adjustment of Status.