Is repenting of/turning from sin a works based salvationism?
Let's search the Scriptures:

The works of the people of Nineveh, was they turned from their evil way

Jonah 3:10 KJB📖
And God saw their works, that they turned from their evil way; and God repented of the evil, that he had said that he would do unto them; and he did it not.

What works of turning from evil way did the people of Nineveh do? When we look at Jonah 3:5-9 KJB, we see all specific works of turning from sin that they did, which are mentioned below:

-They (people of Nineveh) proclaimed a fast
-They put on sackcloth
-The king of Nineveh laid his robe from him, covered him[self] with sackcloth, and sat in ashes.
-The king of Nineveh and his nobles proclaimed and published the decree to not let man or beast, herd or flock, to taste anything, feed, or drink water, and that man and beast be covered with sackcloth, cry mightily unto God, and turn from their evil way and the violence in their (people of Nineveh's) hands.
-The people of Nineveh, along with the king of Nineveh and his nobles, followed the decree and covered both themselves and all their beasts with sackcloth, cried unto God, and turned from their evil ways and violence, because immediately God sees the people of Nineveh's works that they turned from their evil way.

Jonah 3:4 - 10 KJB
[4] And Jonah began to enter into the city a day's journey, and he cried, and said, Yet forty days, and Nineveh shall be overthrown.
[5] So the people of Nineveh believed God, and proclaimed a fast, and put on sackcloth, from the greatest of them even to the least of them.
[6] For word came unto the king of Nineveh, and he arose from his throne, and he laid his robe from him, and covered him with sackcloth, and sat in ashes.
[7] And he caused it to be proclaimed and published through Nineveh by the decree of the king and his nobles, saying, Let neither man nor beast, herd nor flock, taste any thing: let them not feed, nor drink water:
[8] but let man and beast be covered with sackcloth, and cry mightily unto God: yea, let them turn every one from his evil way, and from the violence that is in their hands.
[9] Who can tell if God will turn and repent, and turn away from his fierce anger, that we perish not?
[10] And God saw their works, that they turned from their evil way; and God repented of the evil, that he had said that he would do unto them; and he did it not.

At this point, this is when the repent-of-sins-to-be-saved crowd & the turn-from-sins-to-be-saved crowd, will attempt to use Jonah 3:9-10 to claim "see, turn and repent are right next to each other, so repent is turn and thus to repent is to turn from sins to be saved".
However, they ignore the biblical fact that when Nineveh's king said "Who can tell if God will turn and repent" in the first half of Jonah 3:9, the second half/part of Jonah 3:9 reveals that the king of Nineveh pleaded and wanted God to turns from this - that God turn by turning away from His fierce anger, not from sins, so that the king, his nobles, and Nineveh's people would not perish.

Who can tell if God will turn and repent, and turn away from his fierce anger, that we perish not?
Jonah 3:9 KJB

Turning from evil ways is a work (Jonah 3:10). Evil ways are sins as per 2 Kings 15:27 - 28 KJB & 1 Kings 13:33-34
In the two and fiftieth year of Azariah king of Judah Pekah the son of Remaliah began to reign over Israel in Samaria, and reigned twenty years. [28] And he did that which was evil in the sight of the LORD: he departed not from the sins of Jeroboam the son of Nebat, who made Israel to sin.
2 Kings 15:27-28 KJB

1 Kings 13:33-34 KJB
After this thing Jeroboam returned not from his evil way, but made again of the lowest of the people priests of the high places: whosoever would, he consecrated him, and he became one of the priests of the high places. [34] And this thing became sin unto the house of Jeroboam, even to cut it off, and to destroy it from off the face of the earth.

Conclusion: Turning from evil way/sin is a work.

@RepentanceExamined