I haven't seen the Darko video but I think you wonder why the interface shows a circle with a checkmark, which used to indicate multi-room support AKA Airplay2, right?
I tested my Airport Express with the 7.6.9 firmware too and on iOS 26 it is like this:
1. Devices like HomePod, Wiim Mini and Mac that support multi speakers show as circles and they can be checked at the same time:
View attachment 491429
2. Airport Express shows the same circle and checkmark too, but as you can see, when it is selected none of the other devices show their empty circles, so it seems to be a single select option like the solo checkmark that was used I guess in earlier iOS versions.
View attachment 491430
And I tried playing from Airport Express's 3.5mm aux output and Apple Music sounded just fine for me.
I don't have a mini Toslink adapter to check its optical output though.
My Airport Express is A1392 though.
OK I know this thread is many months old, but I have to speak up.
First of all, if you are using the audio output of the (very old, I know) airport Xpress, which means that your are using the DAC inside the airport express. That DAC is probably fine, but my God are you leaving so many ones and zeroes on the table!
You dont have to ask me how I know, because I WILL TELL YOU!

The last great effort I made to build an audiophile stereo system was 20 years ago, and it was airport express based.
Now, lets get some of the uglies out of the way: The Apple Airport Express is a bit perfect digital audio transceiver, but its jitter is horrendous. An absolute jitter bomb.
So, many moons ago I built my A$$ kicking audiophile system. I had a PowerMac G3 which I ripped all my music to. To play music my iTunes app sent digital audio over my home ethernet network to my airport express in my man cave with the stereo. The Airport Xpress had a toslink cable to connect to my DAC which connected to my stereo. My stereo system was..........OK....pretty good. I am going off memory and I dont remember many details, but I had this german DAC, I remember how it boasted its ability to address and fix jitter. It turns out that at the time (early 2000s) many manufacturers were boasting about how they could fix jitter. Most didnt, including the maker of my DAC. My DAC then fed a Behringer amplifier (my God! How can I be serious about audio with.....THAT?) which ultimately fed some Wharfdale towers with dual 8" woofers (I LIKE BASS.) I remember how I gleened that the Wharfdale towers with its dual 8s, assigned different duties to each 8"driver. The lower 8" woofer was doing normal bass duty reproducing the lowest bass frequencies as expected, but the upper 8" was performing a more midbass duty, and perhaps some midrange too. Odd. But damn those speakers sounded good. I loved them. OK So I had my system, and as my digital music server it sounded..............OK. Nothing special. So I read up more and more about how jitter is the enemy of digital audio, and I started my pursuit on devices that could address that. I came across this website, Empirical Audio. The man behind it was Steve Nugent. I read forum posts by him and he was talking about how he addressed jitter head on. A bit arrogant, I suppose. Talking smack like a pro wrestler. Further research about his products, though, and it showed that with the off ramp in particular, he knew what he was talking about. I wanted an off ramp, badly. I had a feeling that the digital output of my airport express was the weakest link. His off ramps cost quite the pretty penny at the time, but I found a 1st gen offramp (apparently before Mr. Nugent made it big) on craigslist for like $100. It only addressed jitter at 44.1Khz, which was fine by me.
I bought it. I got the extra TOSlink cable to feed the airport express's digital output to the offramp, then the offramp fed my DAC.
The result?
Dear me.
My God.
Holy Moly.
It was as if the airport express was feeding grapes to the offramp and out the other end came the best wine you ever tasted.
Holy EEFFing S%$^#&t audio products, Batman!
I was completely stupified by how wonderful that one device made my system sound. You know, if my house burnt down:
I could replace the amps
replace the DAC
replace the speakers.
But that OffRamp? From my cold dead hands.
And lastly, why the Behringer amp? POWER. For cheap. I also did this mod on the amp to slow down the fan speed and make them very quiet. My stereo sounded good, but wasn't 3 dimensional holographic at all. Im pretty sure that was because of the Behringer.
Lastly, I had 2 airport expresses. I learned that the EMI of the airport express would interfere with its other circuits, so I had one airport express doing WiFi duties (from another room) and the other airport express exclusively transceiving digital audio. I always found it interesting that Apple included a software switch to turn off the WiFi radio transceiver in the airport express. Hmmmm.
Anyway so that's my story. And the moral is:
1. GET A TOSLINK CABLE for your airport express.
2. Get one of those jitter reducing units. I believe they are now referred to as DDC (digital to digital converters.)
3. Steve Nugent is my Digital Audio hero.
