If you can get each computer onto the Internet without re-cabling, you already have a data highway. it is provided through the SWITCH functions of your Router, and does not actually send any information onto the Internet to accomplish these transfers. This uses the networking capabilities of you two Macs, with your Router directing traffic. File Sharing is widely compatible among a large span of MacOS versions over time.
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If you prefer to add a cable, it must be a Networking cable. Ethernet and Thunderbolt can be used as networking cables. USB-C is a local peripheral cable, and will generally NOT suffice for File Sharing.
for ThunderBolt transfer, you may need to manually add a ThunderBolt Bridge device is System preferences > Network on each Mac. Ethernet is usually is already shown there.
The ultimate in simplicity is 'sneaker-net'. With this method, you drag and drop the files onto a USB thumb drive, or any connected drive, then eject the drive and carry it (using the sneakers on your feet) to the other Mac, and plug it in there, Then drag and drop files from the USB thumb drive to your folders.