MacBook Pro M1 PRO WiFi 2x slower than other devices

The report you posted shows that you have remarkably high RSSI (Raw signal strength) at -36. you must have been right next to your Router.

Using 802.11ax in the 5GHz band on channel 149, your connection achieved a transmit rate of 1200 M bits/sec by using the highest encoding rate possible (1024 patterns per signaling interval) using two antennas.

The main reasons users do not achieve their throughput potentials under what appear to be great conditions, comes down to two things:

1) too much junky software running:

If you have installed software that wastes computer resources on a regular basis, such as third-party Virus Scanners, speeder-uppers, Cleaner-uppers/Removers, Optimizers, third-party file Sync-ers such as DropBox, BackBlaze, OneDrive, or GoogleDrive, or a VPN that you installed yourself, it will do busywork at previously-impossible speeds.

The way to run a test that eliminates that as a possibility is to run the speed test in Safe Mode.

"Works OK in Safe Mode, fails in regular mode" implies "It's something you added."

2) interference from other devices in your 'network neighborhood'

802.11ax uses more complex modulation schemes, especially a higher number of patterns per signaling interval. This makes it MORE sensitive to interference and collisions from neighboring networks using nearby channels.

It is important to understand that, despite your choosing 149 as your nominal transmit channel, your 80 MHz data pathway uses spectrum from channel 149 to 161. ANY other nearby devices using any part of that spectrum could cause data collisions that would slow your effective speeds.

https://en.wikipedia.org/wiki/List_of_WLAN_channels

<< If I'd have any interference or other type of radio signal problems, it would affect all connected devices. >>

Not so fast.

if your other devices are running 802.11ac, the length of one signaling interval is substantially shorter (3.2 microseconds duration), while 802.11ax is substantially longer (12.8 microseconds duration).

Interference that occurs while using 802.11ax (Wi-fi 6) is much more likely to clobber your data, and for more than a few bits damage, require re-transmitting the entire packet, and possibly those after it.

At these speeds, you should be experimenting with packet length that is LONGER than the default 1500, to increase throughput if there is no competition. (Stay under 8000, or you need to make a change inside MacOS.)

there are two ways to get an idea of what is around you.

If you hold the Option key while clicking the Wi-Fi icon on the menubar, it shows a sub-menu. Selecting 'Wireless Diagnostics' off that sub-menu launches the Wireless Diagnostics App.

wireless diagnostics > Window > Scan ...

show a list of visible networks around you and it can be sorted by channel:

As I noted above, your nominal channel 149 uses spectrum from 149 through 161.

a very handy inexpensive Utility is available with a graphic representation of Spectrum. It is called WiFi Explorer, available on the Mac App store and has a free trial period.

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those magazine articles suggest the problem is solved for last version of Monterey and current Ventura.

Is that what you are running?

yes, MTU.

At higher speeds, one issue that starts to impact overall throughput is number of frames/packets/blocks outstanding before ACK.

Provided the connection is trouble-free, larger blocks get more data through faster, and spend less time waiting for the ACK from the other end.

My Verizon FIOS Router also has that limitation. it won't accept any setting higher than the default 1500. My other networking equipment that supports fast Ethernet can go much larger.

This is just a subtle side issue, and should not have a large impact on your current experiments.

I think that is used for AirDrop and similar features.

How did you think to look there?