When attempting to use the /summon command, "painting" is not a recognized entity name. This results in a "Syntax error: Unexpected "painting": at "/summon >>painting<< [coordinates here]"" error message. "painting" also does not show as a suggested/valid argument as other entities do.

To reproduce, use the /summon command with the entity painting as the argument.

In one image, I included "\summon" messages in the chat to show what command was typed into the chat to produce the above error message. The second image shows that "painting" is not in the list when typing "pa-".