I have a MacBook Pro. I need to back up my MacBook Pro due to the screen inside is apparently cracked. therefore I am told I have to send it off. I purchased another newer MacBook Pro NOVEMBER 2021. HOW DO I BACK UP MY ENTIRE OLD MacBook Pro

Get an external drive. Use TimeMachine (Apple product) and let it run as long as it takes which may be a couple of hours. I like CarbonCopyCloner (bombich.com, $40) that duplicates the entire drive by detecting partitioning and looks like your internal directory structure.

Either one will give you access to your old files on demand. TM needs an active system (recovery, full boot) to read and you need to be sure the "reading" system is NOT using that drive for its TM to avoid overwrites. CCC is just another external disk with files, as far as file recovery is concerned.

I will not bore you with many external drive selection details given the timeline, but I will say G-drive from Seagate (big orange bumper, at Best Buy) is good, and might as well buy one 2x the size of your internal drive. Do not buy 8 GB necessarily for a 4 TB drive if less than 4 TB used, but I would buy at least 2 GB for a 1 TB drive.