New 2023 Macs - VERY slow internet upload speed?

Whatever’s going wrong with that 2023 is not due to overt problems with the Wi-Fi network.

What networking gear (router) on the other end of this connection? What firmware version is loaded? Current?

Do these Macs misbehave on other Wi-Fi networks running Wi-Fi 5, Wi-Fi 6, or layer?

How many other Wi-Fi networks are in the area?

Any other add-on security apps or any add-on VPN client apps on that Mac, or on that router?

every Wi-Fi based Mac exists in a Space using shared radio waves and subject to interference from nearby devices, as well as software interference. it make take individual analysis to help determine where the problem lies.

Hold down the Option key while you click on the Wi-Fi icon on the menubar. Run wireless diagnostics as a check for GROSS issues in configuration. (Note: if Apple support did not have you do this previously, you did not get adequate support, and need to ask for a specialist to contact you.)

Start over. Hold down the Option key while you click on the Wi-Fi icon on the menubar. you get a snapshots of current operating conditions like this older one: Screenshot, photograph, or transcribe the values seen there and post in a reply to this discussion for analysis:

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Based on that 50 megabits per second reference, is your Wi-Fi router Wi-Fi 2 or Wi-Fi 3? That’s really old Wi-Fi gear, if so.

What networking gear on the other end of this connection?

What firmware version is loaded in the router? Current?

Do these Macs misbehave on other Wi-Fi networks running Wi-Fi 5, Wi-Fi 6, or layer?

Or on wired?

If you’re using HotSpot, that can be heavily throttled by the carrier, among other issues.

surprisingly, the 2017 MacBook Pro has latched onto channel 1 on 2.4 GHz Wi-Fi. it is is supposed to connect to the best signal available, and if that is the best signal available, it makes me wonder why. It has made a connection using 802.11n rules, using a 20 MHz wide channel with 64 patterns per signaling interval on two antennas. it is supposed to have three antennas, and be 802.11ac capable, but maybe not on the 2.4GHz band.

I suggest you turn its Wi-Fi OFF, Restart it, and see what band and what channel it ends up on. Maybe we will learn something.

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the 2023 MacBook Pro has a good raw signal (RSSI) of -63 dB, with noise at a reasonably low -93 dB. You have connected in the 5GH band, making an 80 MHz wide connection on channel 35 using 802.11ac rules. The connection is using 16 patterns on its two antennas (it only has Two) to attain 390 M bits/sec.

The 2017 iMac with comparable signal strength and comparable noise has made a connection with 64 patterns per signaling interval on its three antennas and attained a speed of 878 M bits/sec. Quite a bit faster, and not explainable with number of antennas alone.

On any of these connections for any of these computers, you would still exceed the paid-for upload used of nominal 50 M bits/sec. Something else is going on here, that is not reflected in these data alone.

¿Are all these Macs co-located?

Here's a somewhat newer (expurgated) image of what the macOS Wi-Fi detailed display looks like.

All the signal-related data shown is the same, though the format differs.

This screenshot from a Wi-Fi 5 Mac running macOS 13 connected to a WPA2/WPA3 Wi-Fi 6 network.

(GBA: feel free to swipe this.)

I WILL!

Thank you for producing and posting it.

as a 'demo' of analysis:

The signal strength is Really strong at -27 dB, and Noise at a very nice low -95 dB. you must be very close to your Router, with no interference from nearby peripheral devices or classic noise-makers like microwave ovens.

Your 40 MHz channel is using the maximum modulation technique possible for 802.11ac, using 256 patterns and three antennas. Any interference or users overlapping into your channels, would knock that maximum possible data rate and modulation technique back to something with fewer patterns.

That it is from Mac that has three antennas, but limited (by the model Mac) to 802.11ac. The next higher modulation family, 802.11ax, could go up to 1024 patterns per signaling interval, but that is VERY fragile and any interference will cause that maximum pattern to be unreliable, and it will fall back to one that is more stable.