Power drain and overheating with modern standby

Fully agree with architypitect. This is a disaster and they treat the laptops as smartphones nowadays. If they like the "Modern Stand By" that much, it can exist, but it should be an option to select the normal S3 as well!!!

Modern standby should definitely only be an option, not mandatory.

Still no reply from Dell, and the FAQ still says to never put a laptop in a case or bag unless fully powered down.  My laptop still runs itself at weird times when closed/closed, and it's noticably warm after being closed on my desk all night.  Thought being portable was a fundamental feature...

Which XPS do you have?  I've seen several reports of that registry tweak breaking something with incompatible BIOS versions, leaving people unable to boot until they reinstall.

Have you tried re-enabling S3 sleep? It took some tinkering, but I managed to do it by editing the registry here: https://www.dell.com/community/XPS/How-to-disable-modern-sleep-S3-on-a-dell-laptop-in-2021-S0-sleep/td-p/7838808

Also, I added CsEnabled=0 to the Power Folder, and re-enabled relevant power settings in the registry. (Disconnected Standby, Network Connectivity in Standby, USB Selected suspend (disabled), and disabling wake-timers). Now, my PC goes to sleep, and waking up takes a few seconds, but when it's supposed to sleep, it's asleep.

So I've been chatting with support just to see if there are any alternatives.  They recommended using hybernate, which I had to enable in gpedit and the old control panel.  Unfortunately my system crashes 50-80% of the times it tries to hybernate.  Reliability report doesn't show much exept for "unexpectedly shut down".  When they couldn't diagnose that they suggested installing a modern standby update from Aug 2019 for a completely different laptop and earlier version of Windows.  So yeah, don't get your hopes up.

I have the same issue on my new 2021 Dell Vostro 3500 11Gen, win 11 21H2 installed. Laptop gets hot when in sleep mode and does not respond to wake. All my unsaved work are lost. Dell BIOS does not have option to disable S0 and enable S3. Dell are you even listening??

C:\Users\Dell>powercfg -a
The following sleep states are available on this system:
Standby (S0 Low Power Idle) Network Connected
Hibernate
Fast Startup

The following sleep states are not available on this system:
Standby (S1)
The system firmware does not support this standby state.
This standby state is disabled when S0 low power idle is supported.

Standby (S2)
The system firmware does not support this standby state.
This standby state is disabled when S0 low power idle is supported.

Standby (S3)
The system firmware does not support this standby state.
This standby state is disabled when S0 low power idle is supported.

Hybrid Sleep
Standby (S3) is not available.

So the FAQ I referenced in my original post has been updated with troubleshooting tips, but most of the options referenced there are not for an XPS 17 or available under Windows 11.  Others are just methods of shutdown (defeats the purpose of sleep) or diagnostic (confirming S3 sleep not available) without any actionable steps.  The option to disable network on sleep doesn't exist in this version of Win11 either.

Meanwhile Dell Support keeps asking me to re-install Windows, but I don't see any reason that would work.  In any case, I did a month ago for other reasons and had these issues before and after.

My company has Dell as primary laptop supplier for the last decade+

With this, I am recommending my boss to drop Dell until they fix it. Our head of IT agrees with me. 

Do the same in your company. Money is only thing Dell will understand. 
(For the record I used dell laptops for most of my professional life and consider them superior to other brands, but this is just too much)

I'm on my 5th, yes 5th Inspiron (latest 16 Plus).  I had no idea what Modern Sleep was until I mentioned my laptop fans spin up (sometimes) and overheats (always) when closing the lid.

Disabling modern sleep fixes it, but then I don't have instant on.  Looks like there is still no fix from Dell so I will be moving on from Dell.  It's not a Windows issue; modern sleep works fine on my other laptops, work and personal.

How did you disable modern sleep? The community faq post I'd linked has been updated with even stronger language saying it's the only sleep option, and that we should never put a laptop in a case without powering it off. Hope no one ever needs to carry their laptop around for meetings...

Finally, something a (little) more concrete.  LTT's latest video (https://youtu.be/OHKKcd3sx2c) explores the issue and takes a crack at a workaround: unplug your laptop before closing the lid, since network/updates/etc remain active when slept when AC connected, and doesn't switch when unplugged while sleeping.  I've never considered buying a MacBook before, but if this dumb issue is still around in another year I might have to.

In case anyone is wondering, this is still not fixed.  If I put my laptop in a bag without fully powering it off, there is a significant chance it will burn through the battery trying to cook itself.

Oh my, thank you all, as I have been searching for this for 6 months since I purchased an XPS recently. Dell support has treated me like they have no knowledge of this. Super frustrating and has me off Dell as well - even more so since they have known about it for 2+ years. I have spent sooo much time trying to go through configs to avoid this - and it always came back. Time to request replacement... or better yet, refund!