I you don’t see built-in speakers as an option in System Preferences / Sound.

hcsitas wrote:

The built-in speaker is not an option - it only works if there are no sound devices present.

The built-in speaker is not an option if something is plugged into the headphone jack. But on my Mac, I have

• External speakers, plugged into a USB sound card
• A headphone, plugged into the headphone jack

Unplugging the headphones gives me the option to choose between the internal speaker and the USB sound card. So it seems like it is the built-in outputs (speakers, analog headphones, optical digital output) which are subject to the "either-or."

kristof36 wrote:

The iMac does not have an optical digital audio output.

According to Apple, an iMac (21.5-inch, Mid 2014) does have an optical digital audio output. The headphone jack is a combination "Headphone/optical digital audio output (minijack)" – just as I guessed.

iMac (21.5-inch, Mid 2014) - Technical Specifications

Also no headphones plugged in.

If there is nothing plugged in, that suggests that there is some dirt inside the port, or something bent inside the port, that is fooling the iMac into believing that an optical digital audio cable is plugged in.

There is a micro switch inside of the headphone port that switches the audio from internal to external when headphones, buds or a speaker system is plugged into it.

Either the micro switch is stuck, the micro switch is permanently stuck or there is a broken off piece of a headphone jack stuck in the headphone port.

If the micro switch in the headphone port is just stuck?

Try plugging and un-plugging headphones several time to see if it will unstick.

If the micro switch in the headphone port is permanently stuck?

Then the headphone port needs to be repaired.

If there is a broken off piece of a headphone jack inside of the headphone port?

Then the piece needs to be removed or headphone port need to be repaired.

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Automatic translation: "digitale uitvoer" (Dutch) == "digital output" (English).

By any chance, do you have a Mac with a headphone jack that has the ability to double as a S/PDIF (Mini Toslink) optical digital output? And is an optical digital audio cable plugged into that jack?

https://www.macworld.com/article/230254/how-to-replace-the-missing-optical-digital-audio-output-on-newer-macs.html

On my Mac, when I plug something into the headphone jack, the "Internal Speakers" changes to "Headphones."

EDIT: I'm certain that's it. The translator says that "optische digitale uitgang" means "optical digital output".

What’s that USB cable connected to?

hcsitas wrote:

Yes, that’s normal. Continue with your headphones; the very basic, mono internal speaker is not meant for anything other than system chimes and stuff. It is not an option in your setup.

Many Mac Minis (like the one someone was recently asking about in another thread) have a very basic, mono speaker. A mid-2014 21.5" iMac has stereo speakers.

Yes, that’s normal. Continue with your headphones; the very basic, mono internal speaker is not meant for anything other than system chimes and stuff. It is not an option in your setup.

The built-in speaker is not an option - it only works if there are no sound devices present.

Yes, that’s what I meant - built-in.

👍 Sorry, my bad 😁