Well, you got me to look it up myself. I think it was both.

From CNN, Sept 17:

“Regardless of ABC’s plans for the future of the program, Sinclair intends not to return Jimmy Kimmel Live! to our air until we are confident that appropriate steps have been taken to uphold the standards expected of a national broadcast platform.”

From Deadline, Sep 17(worth a full read):

The two largest station groups, Nexstar and Sinclair, wielded their influence over ABC‘s decision to pull Jimmy Kimmel‘s show from its ABC stations.

Nexstar strongly objects to recent comments made by Mr. Kimmel concerning the killing of Charlie Kirk and will replace the show with other programming in its ABC-affiliated markets.”

Nexstar’s announcement was followed soon after by ABC’s decision to pull the show indefinitely.

Sinclair Broadcast Group, the largest of ABC’s affiliate groups, said that it also objected to Kimmel’s comments, and said that it would “not lift the suspension of ‘Jimmy Kimmel Live!’ on our stations until formal discussions are held with ABC regarding the network’s commitment to professionalism and accountability.” It also called on Kimmel to make a direct apology to the Kirk family, and for the network to make a “meaningful donation” to them and Turning Point USA.