Why does macOS prioritize Wi-Fi over Ethernet for file transfers after turning off Wi-Fi?

I’d wonder if the network setup is incorrect, or if Wi-Fi interference is high.

How many IP routers here? More than one router? Or is the network using Access Points?

A recent Wi-Fi network with low to moderate levels of interference will outrun gigabit Ethernet.

On Mac, the basic Wi-Fi environment characteristics are visible when using Option-Click on the Wi-Fi logo 🛜 in the menu bar to capture some Wi-Fi network data.

For us to look at the Wi-Fi network data here, post the items shown in the following image including the Security mode and from Channel to NSS inclusive (Security, Channel, Country, RSSI, Noise, Tx Rate, PHY mode, MCS, NSS, green highlight) (without posting the Wi-Fi address, any local HotSpots that might be present, the network name, or the BSSID, all of which are expurgated from the image shown below, red highlight), and we can take a look at the basic network environment.

Tools such as the third-party WiFi Explorer app for macOS can be used to get a better view of the environment.

Your particular Wi-Fi might also have some monitoring capabilities.

My experience is that Ethernet always becomes the default interface if it is active.

WiFi might be used if and only if it is the only path to the device, or as in the case of AirDrop, and Ad-Hoc network is created.

Check your Service Order

Interesting. My experience is different. I have ethernet at the top of the order but I always have wifi on as I use dropbox quite often. I never turn off and my system always uses the ethernet connection since it is ordered that way. Not sure why yours would be any different but I do not have any NAS in use which may be the reason. I have a Mac Mini M4. Seems like the service order would take precedent over any other setting. Perhaps the router has some impact?

MrHoffman wrote:

A recent Wi-Fi network with low to moderate levels of interference will outrun gigabit Ethernet.

I'd like to understand more about that. Here's my question ...

How could that be unless the WiFi clients + the WiFi access point (router) are all operating in close proximity on a clear 6 Ghz channel? It seems to me that the end-to-end throughput between 2 WiFi clients connected through the AP on 6 GHz (with its potential 2 Gbps speed) would only be an effective 1 Gbps max. And a WiFi-to-wired transmission would be limited by the wired back end, which in most cases is 1 Gbps max? How would it outrun gigabit Ethernet?

Wi-Fi 6E 6 Ghz tops out just shy of 10 Gbps with sufficiently-wide channels and streams, and Wi-Fi 7 tops out past 20 Gbps.

What wired I’m dealing with is a mix of 2.5 Gbps and 5 Gbps, though with GbE used in parts. If your switches are GbE, yes, that will throttle.

Check if your NAS supports link aggregation too, 802.3ad or otherwise. The local Synology boxes with multiple GbE ports include that.

If I understand that correctly, you would need to bond up to eight 6-Ghz channels in order to achieve that potential speed. Even then, does it even work at any distance greater than 20'-25' from the AP? Through a wall? Is there any consumer gear that can do that?

In my setup Network service order Ethernet > Wi-Fi is honored. Have you tried to fiddle it back and forth to anther setting and maybe doing a reboot in between?

Sorry, I meant Airdrop not dropbox.