Ethernet keeps Dropping (not Wifi which is Stable)

After giving it some thought, have you setup a VPN on your Mac by any chance? This looks like what happens when the VPN drops and kills all connections so you then have to turn your network connection on and off.

Does it only happen with your Mac? Do you have other devices to test that USB-C ethernet adapter you are using? You could do that with an iPhone 15 or an iPad Pro (first gen in 2018 was USB-C already).

Another thing that caught my eye, you mentioned "15" MacBook "Pro" swapped for M2 by Apple Ireland". Did they give you a refurbished one or a new one? If it's new, did you get Apple Care+? If you are still covered then they should look into the issue under that cover.

If none of this helps, I guess you could always book an appointment at an Apple Store's Genius Bar to see if they can help. You can use the get support link there Official Apple Support

Actual Speed:

The good way to check the actual connection speed USED to be Network Utility, But in Catalina and later, Apple has deprecated Network Utility and now you have to use a Terminal command to see your actual connection speed. First, you need to know what en number the link is. then you use a command like this one, substituting the actual en number.

my main Ethernet connection uses BSD name en2 (as shown in) :

 menu > about this Mac > (system report) > network:

Aquantia AQC107-B0:

Name: ethernet

Type: Ethernet Controller

Bus: PCI

Slot: Slot-3

Vendor ID: 0x1d6a

Device ID: 0x87b1

Subsystem Vendor ID: 0x1d6a

Subsystem ID: 0x0001

Revision ID: 0x0002

Link Width: x4

BSD name: en2

Kext name: AppleEthernetAquantiaAqtion.kext

Location: /System/Library/Extensions/IONetworkingFamily.kext/Contents/PlugIns/AppleEthernetAquantiaAqtion.kext

Version: 1.0.64

Terminal command:

ifconfig en2 | grep media

with this as my output for 10 Gigabit Ethernet:

media: 10Gbase-T <full-duplex,flow-control>

For ‘regular’ Gigabit Ethernet, you should get this instead:

media: 1000baseT <full-duplex,flow-control>

Errors detected:

To see if an Ethernet link is throwing more than a handful of initial errors, you can use Terminal command:

netstat -I en2

This is the resulting output. Counters are In-packets, In-errors, Out-packets, Out-Errors, Collisions. There should never be more than handful of errors from starting up, and in most cases, NONE.

Name       Mtu   Network       Address            Ipkts Ierrs    Opkts Oerrs  Coll

en2   8163  <Link#4>    00:01:d2:1a:00:dd   696697     0   484301     0     0

en2   8163  grantsmacpr fe80:4::461:ea0d:   696697     -   484301     -     -

en2   8163  192.168.0/23  192.168.0.204     696697     -   484301     -     -

Reading the top line, If the link were running beyond its ability to run and be stable, for example it auto-speeded to 10Gb but the cabling could only reliably support 2.5Gb, we would see non-zero errors counts, and errors increasing over time. (and possibly, disconnecting)

one other very obscure issue some reader have reported, is bent pins in the connector, and I suppose dirt on those pins could be an issue as well. To check, get a bright light and inspect the pins in the socket for straightness and no sign of foreign matter.

can you please post a screenshot of

System Prefrences > network

this is a MUCH older one:

..

Ethernet usually connects once, incurs no transmission errors, and runs solid as a rock, at its connected speed, forever. If you had a marginal connection is some way, such as a marginal cable, the numbers would creep slowly upward over time.

A cable that is BAD or a port that is BAD typically causes a sudden disconnect. Those counters are quite large, and can record a lot of packets or errors. I think they might start over when your Mac wakes up or starts up.

<< ethernet constantly dropping out >>

how did you decide that?

please post a screenshot of the screen that told you that.