You can run clonezilla on your shell session, just apt install conezilla (or whatever variant you’re using) and it can do the trick. Dd will almost surely work too, but that leaves a ton of responsibility to you instead of making any sanity checks on the way. That makes dd very powerful tool and it has saved my ass a multiple times, but if you already have a working partitioning schema clonezilla has a ton of options to make your life a lot simpler and a likely a bit faster than dd.

Yes, Clonezilla runs off a live USB. If it is large enough it can also store the partition you want to clone, making the whole process a lot simpler.

Use a clonezilla boot usb. I did exactly what you’re trying with clonezilla: 16gb partition on a 128gb ssd to a 64gb ssd. The clone disk is in a production machine rn and has been for two months.