No it wasn’t. Gerrymandering that demonstrably targeted racial or other protected demographics or otherwise broke the voting rights act was illegal. But gerrymandering as a concept has never been illegal in the US. State and federal courts, including SCOTUS, have ruled several times that there is no constitutional law against it, nor a mechanism to objectively identify it, nor a means to remedy it. If it violates those other laws in the process, it gets rejected and kicked back to be fixed. But if not, there is nothing illegal about it under current law, despite it being blatant vote manipulation. What SCOTUS has rolled back is certain oversight for the voters right act and have given legislatures the out to claim that blatant racial disenfranchisement is political, not racial.

Edit: There might be individual state laws or constitutions making gerrymandering illegal or otherwise removing the districting power from the legislature. I’m not aware of any, specifically, but I wouldn’t be shocked if there were. I’m only speaking on a federal level.