The law in Number 4 is very strict:
17The Lord said to Moses and Aaron, 18“See that the Kohathite tribal clans are not destroyed from among the Levites. 19So that they may live and not die when they come near the most holy things, do this for them: Aaron and his sons are to go into the sanctuary and assign to each man his work and what he is to carry. 20But the Kohathites must not go in to look at the holy things, even for a moment, or they will die.”
The situation in 1 Samuel 6:19 was slightly different. The ark was being transported. The transportation was prepared by the Philistines, not by the Levites. It was exposed to sight. It arrived at Beth Shemesh in
1 Samuel 6:
13 Now the people of Beth Shemesh were harvesting their wheat in the valley, and when they looked up and saw the ark, they rejoiced at the sight. 14The cart came to the field of Joshua of Beth Shemesh, and there it stopped beside a large rock. The people chopped up the wood of the cart and sacrificed the cows as a burnt offering to the Lord. 15 The Levites took down the ark of the Lord, together with the chest containing the gold objects, and placed them on the large rock. On that day the people of Beth Shemesh offered burnt offerings and made sacrifices to the Lord.
No problem, so far so good, but then:
19 God struck down some of the inhabitants of Beth Shemesh, putting seventy of them to death because they looked into the ark of the Lord.
Did they looked into or looked upon the ark of the Lord?
They had looked upon the ark of the Lord when it arrived in verse 13. Now, some of them were punished probably because they had looked into it.
At https://biblehub.com/1_samuel/6-19.htm, 1 version uses "looked upon", 1 version uses "gazed upon" and 21 versions use "looked into" or "looked inside".