What he did is sign the bill but tells Congress that, unless certain things are removed, his signature is null and void:

As President I am demanding many rescissions under the Impoundment Control Act of 1974. The Act provides that, “whenever the President determines that all or part of any budget authority will not be required to carry out the full objectives or scope of programs for which it is provided, or that such budget authority should be rescinded for fiscal policy or other reasons (including termination of authorized projects or activities for which budget authority has been provided), the President shall transmit to both Houses of Congress a special message” describing the amount to be reserved, the relevant accounts, the reasons for the rescission, and the economic effects of the rescission. 2 U.S.C. § 683.

I will sign the Omnibus and Covid package with a strong message that makes clear to Congress that wasteful items need to be removed. I will send back to Congress a redlined version, item by item, accompanied by the formal rescission request to Congress insisting that those funds be removed from the bill.

I am signing this bill to restore unemployment benefits, stop evictions, provide rental assistance, add money for PPP, return our airline workers back to work, add substantially more money for vaccine distribution, and much more.

https://www.whitehouse.gov/briefings-statements/statement-from-the-president-122720/