You might be lucky and solve it by inspiration. When that fails, fall back on a careful, thorough and systematic approach as explained here.
ethernet
Summary of AirDrop, network file sharing, target disk mode, and sneakernet, explaining how to use each and what they’re best at.
AirDrop is quick, convenient and as slow as you’ll get. Ethernet all too often runs at only 1 Gb/s. Here are the fastest solutions involving M1 models.
Backing up using Time Machine over Gigabit Ethernet to another Mac providing shared backup storage in Monterey 12.1 delivered good performance of 35-43 MB/s.
Even if you don’t connect it, a Mac’s Ethernet port is vital to authorise it to the App Store and more. Here’s how to cope if it goes missing.
Sunday morning nightmare: how a missing component of OS X brought my iMac to its knees.
Does it help to unplug your network connection when checking suspicious email?
How does creating a new location in the Network pane solve network lockout problems?
How can I extend the WiFi range of our Home Hub into the nearby cottage, through thick granite walls?
How can I locate a break in an Ethernet cable running under a floor?
The Eclectic Light Company 