Optimized charging not working in Sonoma?

You are over-worrying this. As others have pointed out, even in desktop mode or after being at 80% for some time, it will once in a while charge up to 100% and be there for a while then go back to 80%. Also, sometimes it stops at a different level than 80%. Like 76%. Or something else. Staying all the time at 100%, or 80%, or some other value is not ideal for this type of battery. So the OS tries to vary things some and periodically it "exercises" the battery, research has shown this can extend the life of the battery. Since we don't have access to the "algorithm," we can't tell why it is doing what it is doing and when it might change things. Also, Sonoma MIGHT have updated the algorithm (versus other OS versions), so just because something changed does not mean there is a problem with Sonoma.

What you are doing is like obsessively measuring tread wear every day or every week on automobile tires. Laptop batteries, like automobile tires, wear out over time and have to be replaced. The Mac OS is just trying to "drive the car" in a way that maximizes the life time.

Strange thing happened. After fresh system install everything worked for some time. Now it works, sometimes... Optimized charging sometimes kicks in, showing that it is in desktop mode, then every few days it charges fully. Then, again it goes desktop mode. I'm blown. No clue what is going on. Firstly I thought it might be bad cable or short power outage, but it is happening at least for a month. Maybe battery is old, it's time for new Mac.

Batteries are considered Consumable Products. Over time it will degrade to a point where it needs to be replaced. The usage is normal as the capacity will go up and down all the time and never stay always at 100%. Apple Batteries are rated for 1000 Full Battery Cycles and / or 80% Capacity before needing Evaluation or replacement.

For additional reading on Battery and Apple Computers this link may help. About battery health management in Mac notebooks and especially for the M1 / M2 and Big Sur  & Monterey  and Ventura If battery charging is paused or on hold on your Mac

Depending on the Age of the computer, some aspects from the above links, may or may not apply to your computer.

A feature introduced into Big Sur & Monterey, Ventura, Sonoma was to preserve the number of Full Battery Cycles - there was an Algorithm coded into the macOS.

It is perfectly Normal for Big Sur , Monterey, Ventura , Sonoma to Pause / Suspend charging the battery beyond 80% and hold it at that level.

One can nudge / over-ride this by clicking the Battery Icon on Desktop Top Bar and allow charging beyond 80%. From observations, it will Pause / Suspend again once reading 90%. Same procedure to over-ride and will charge to 100%

Image below is from a M2 MBA purchased March 2023 and only now learning to Pause Charging at 80 %

Perhaps the nuance was missed >> " Image below is from a M2 MBA purchased March 2023 and only now learning to Pause Charging at 80 % "

That is Purchase March 2023 and now October 2023 = 7 months, the computer is a Slow Learner

If that is not to your liking

Then have a few suggestions ;

1 - Get Support Choose a product and we’ll find you the best solution.Start now and open an Apple Support Ticket as they are Apple Employees to deal will these types of issues . 

2 - Product Feedback - Apple and make it known to Apple regarding this ongoing issue 

Just be patient, your Mac will learn how you use it and go into the desktop mode with charging on hold, that is, if you keep your MacBook always plugged in.

1. Have Optimised Battery Charging mode and Manage battery longevity enabled,
2. After a day's work, put it to sleep. You don't even have to close the lid. The next morning, just touch any key, and then the Touch ID button to get to your user space,
3. Before putting your MacBook to sleep, quit all apps, if they are not supposed to run unnecessarily.
4. After few days, your MacBook/MacOS will learn how you use it, and act accordingly to safeguard your battery.

Well, here's what Apple say about Optimised battery Charging. It should work that way. I can only tell that my MBP, a T2 one, is doing just that, and it is at 80% for a long time. Maybe, it is something to do with your battery itself, Maksymalna pojemność is 84%. Maybe you should show the MacBook to the technical service.

Do you have this in System Settings > Battery?

Mine is a 2018 15" MBP. The battery charge is at 80%. It is my work/leisure notebook, usually on from 9 to 23, and then goes to sleep until the next morning. Of course, it goes to sleep, when I go out in the day too. So, optimized charging appears to be working.

The Macbook has to stay connected to power continuously for quite sometime for Macbook/MacOS to learn to stay in the "Desktop Mode" as shown in my first screenshot. You don't pull the plug out, or log out, or restart, or shutdown the Macbook for quite a while with optimised charging enabled. When the optimised charging takes over, the drop down menu of the battery icon will look like this,

with that additional "Charge to Full Now," that is, if you want to take the Macbook out to use as a portable notebook. And, once you come back, and plug it in to electrical power, Macbook would go on the learning cycle again, that is, it'd go back 100% and after about 1 and 1/2 days go back to 80%. If that happens, check your System Settings > Battery, to check if it would shows this,

that your Macbook had gone into the Desktop Mode. Then, the Macbook/MacOS had learned how you use the Macbook, and acts accordingly. It took me sometime to learn this.

Opladen in de wacht: Desktopmodus (I think your language is Dutch. Google translation)

The Charger is a 35 Watt Apple Original with the Apple Original MagSafe Cable

The image below indicates the Charger is only giving a charge of 11.63 watts of a possible 35 watts or sometimes references as a Trickle Charge

I personally pay attention to Designed Capacity versus Full Charge Capacity

All else would be micro managing the battery and no time to actually enjoy using the M2 MBA for useful things like replying to this inquiry

Don't use these 3rd party fear-mongering modifier apps!

MacOS can look after herself.

I don't want to use additional software, when I could use function build in the system.

Mine states only that it is fully charged. No desktop mode at all. I haven't disconnected it since last wipe, a week or more.

Musisz być cierpliwy. MacBook/MacOS z biegiem czasu nauczy się, jak korzystasz z MacBooka, a jeśli używasz MacBooka na zasilaniu przez dłuższy czas, po pewnym czasie poziom naładowania powoli spadnie do 80%. Gdy już tam jest i nadal używasz MacBooka na zasilaniu, to jeśli/kiedy używasz Maca na baterii, a następnie wrócisz do korzystania z zasilania, powrót do trybu pulpitu zajmie dzień lub dwa. Następnie powoli powróci do 80% i pozostanie na tym poziomie przy włączonym zasilaniu.

Następnie może powoli wzrosnąć z powrotem do 100% na dzień lub dwa, a następnie wrócić do 80%. Musiałbyś być cierpliwy.

I appreqcieate all your efforts. I do always like you wrote. It always worked until Sonoma update. From this time it's not working any more. I didn't changed anything in my habits.

What is more, I don't have such thing like "Manage battery longevity". And I don't remember if I ever had. But I know for sure that at least for last year this function worked properly. My battery was always charged to 80%.

In time, it'd hold. You have to be patient. Since this image on 14th Dec,

it stays at 80% even after 2 upgrades, 14.2 and 14.2.1. As you all know, there are several reboots while updating, but it didn't go back 100%, but stayed at 80% all the time, sometimes 79%.

Of course, according to Coconutbattery app, it is 75.2%.