‘Aml عملinthe Qur’an usually implies good deeds/works.
Soo’u a’maalahum (سووعأعمالهم)is for their evil deeds.
So shaytan is beautifying for the disbelievers their good deeds. This is what it seems like from the words used.
People do alot of evil deeds, then they might do a small good deed. Shaytan makes them remember the small good they might have done but they forget the huge evils they have also done. So shaytan beautifies this small good, and the person thinks they are really pious, and that this good deed is sufficient for them to be saved from Allah’s punishment.
A beautiful example of this is in surah Shu’ara 26:18-22. Where Pharaoah reminds Moses the favour of his upbringing of Moses when he was a child.