USCIS already approved our I-130. Can they still question whether our marriage is real later?

Yes. I-130 approval is an important step, but it does not freeze the marriage issue forever. Later stages such as adjustment of status, removal of conditions, or naturalization have their own eligibility review. If new evidence or inconsistencies appear, USCIS can look again at whether the marriage was genuine. Keep your records consistent and do not assume the earlier approval makes later questions impossible. Keep important relationship evidence even after I-130 approval because later stages may revisit the marriage.