Power on without power button

What you are seeing is unusual because “Start up when power is connected” is set to “Never.” 

Apple says this feature applies to Mac mini models introduced in 2024 or later running Tahoe 26.5 or later. With Never selected, simply reconnecting the power should not turn the Mac on. Apple: Turn on a Mac mini without pressing its power button

I would first check System Settings >> Sound >> Play sound on startup and make sure it is enabled. 

The missing startup sound is worth checking separately; by itself, it does not tell us why the Mac is turning on. Apple: Turn the Mac startup sound on or off

Next, shut the Mac down completely, unplug it, wait about 30 seconds, and plug it back in. 

If it starts again, try the same test directly from a wall outlet if you normally use a power strip, UPS, or switched outlet.

If it still starts on its own, open Terminal and enter: pmset -g | grep autorestartatconnect

If you see autorestartatconnect 1, macOS is reporting that automatic startup when power is connected is enabled. If you see 0, it is reporting that it’s disabled.

I would not change the setting yet. 

The result is useful because it will tell us whether macOS’s underlying setting agrees with what System Settings is showing. 

If you post the result here, we can determine the appropriate next step without making unnecessary changes. 

If the command returns nothing, run pmset -g instead and post the output.

Knowing what you know and from what has been observed thus far

The next logical step would not Turn Off the power source

Barring that

If you believe you have identified behaviour in macOS 26 Tahoe that does not function as intended or does not appear to work as described in Apple’s documentation, you may wish to report it to Apple as a possible software issue.

Apple can review the report and determine whether the behaviour requires further investigation. To help with that investigation, it is important to provide clear and accurate steps showing how the issue occurred, what you expected to happen, and what actually happened. Apple may also request additional information, diagnostic logs, files, screenshots, screen recordings, or further steps to reproduce the issue.

If Apple decides that the report warrants further investigation, the issue may be examined by the appropriate Apple teams. Those investigating the issue may attempt to reproduce the behaviour under controlled test conditions and determine whether it occurs consistently and whether the reported steps reliably produce the same result.

If the behaviour can be investigated and is determined not to be working as intended, Apple may identify a potential fix or take other appropriate action. However, Apple may also determine that the behaviour works as designed, that additional information is required to diagnose the issue, or that the issue is caused by third-party software or hardware.

For this reason, a clear and repeatable set of steps, together with relevant diagnostic information, is one of the most important parts of an effective report to Apple.

Apple's published guidance specifically recommends providing detailed reproduction steps, expected and actual results, and relevant diagnostic information. Apple also notes that it may request additional information or files while investigating a report. (Apple Developer)

RossoRacer wrote:

Since upgrading to Tahoe 26.7.1 my Mac mini M4 Pro has been staring up when I turn the power on at the wall socket, instead of pressing the power button.

Why are you turning off the main power to the Mac mini...?

Turning off the power, will eventually cause the CMOS to drain out and create more problems.

It also no longer makes the 'booting up' sound. In the ENERGY Section of System Settings the 'Start up when power is connected' is set to NEVER.

Do you have external audio devices connected to the Mac mini...?

If so, disconnect the external audio device and reset the Mac mini internal volume output.

This is very perplexing. Anyone know a solution?

Leave the main power on to the Mac Mini.

Then choose between Shut Down or Sleep from the Apple Drop Down Menu and walk away.

Or optionally disable Automatic Sleep Mode and just let the Display(s) turn off on at a set time.

Personally we leave all of or Mac mini's powered on 24-7 and only allow the Display(s) to turn on the timer.

Why are you using the wall plug as the on/off switch? Leave that on and if you want to turn off your Mac use the power button or the shut down menu. Also check your sound settings to be sure the startup sound is activated.

It looks as though you are not alone. People started noticing the behaviour in certain late Sequoia updates though the feature was only added officially in Tahoe.

There are a lot of online conversations . . . Auto Boot

I have not switched my power socket off so I don't know whether mine would be affected.

Post your question into Gemini AI and it will tell you why it is occurring and give you some quick suggestions using Terminal, including the simple commands you can copy and paste.

I assume you are comfortable using Terminal?

I use Gemini and find it can solve all my problems but it doesn't succeed first time on every occasion.

So you need to interrogate it and when something fails, tell it and it will revise its advice and suggestions which ultimately provide a solution.

It's much quicker than asking on forums but of course it's always useful to use the forums as a backup as AI can get things wrong and its first suggestions don't always work.

Your problem is unlikely to be a bug in Tahoe as it doesn't appear to be happening to anyone else.

RossoRacer wrote:

I've reported it to the Developers as a possible Firmware bug, seeing as others are experiencing it too.

I have a M2 Mac Mini and a M4 Mac Mini both were running Tahoe macOS 26.6.2 ( 25G83 ) Aug 17, 2026 when there was a Area Power failure to lasted about 45 minutes

Both machine were poser off via the Shutdown method

When the electrics was restored, Neither of the machines Auto stated back up

To add to tbirdvet's comments, powering down using the wall socket will damage your Mac . . . I assume you are not doing that?

If you're going to turn the power off at the switch each night then this System Energy Setting should be set to "never":