That report, a couple of lines in a broader article, led to an outpouring of anger, rejection, and also of support for Chabad.

Chabad probably owes Lapid a debt of gratitude for the outpouring of support for Chabad his reported threat caused.  

Lapid denies making the threat, though he is concerned about Ben Gvir getting into the Knesset.

The background for this is the wide support Ben Gvir has among Chabadniks, who are not traditional Haredi voters (they are not traditional Haredi anything, despite the black jackets and hats). Lapid, or at least the report, believes that wide support from Chabadniks might push Ben Gvir over the top into the Knesset.

Even if true 100%, and even if Lapid will win the elections outright and easily form a leftist coalition, and even if everything possible falls into place for Yair Lapid in these upcoming elections, I can't even think of what Yair Lapid could possibly do to Chabad and how he could hurt them and hound them and shut down their Chanuka ceremonies or their other public work. 

The Chabadniks don't put up their menorahs because they found favor in the eyes of the Prime Minister nor in the eyes of any specific MK. They market really well and pull a lot of strings and play every legal move, and do amazing work for Jews all around the world, especially not religious Jews. They have developed tremendous public support and goodwill over the years. They don't need Yair Lapid to like them or agree with them or approve of them for them to do what they do.

If true, this is probably the weirdest, and possibly least effective, threat ever.