Windows 11 deactivated after 24h2 update

I had the same problem - it's these issues that cause people to delay updates. I even took the step to register my device thinking it would safeguard this type of problem, but it wouldn't recognize my machine as valid. Fortunately I had my old documentations and it accepted my same key. But I can see how this will be a major issue for people who are less tech savvy, or have misplaced their docs. In this era, for a tech company to require someone to have a long keystring secured away is crazy.

Adding to the pile, my computer updated yesterday to the 24H2 on Windows 11, deactivated my windows 11 and now I have a horrid watermark that implies I stole. Which I find highly offensive and dismissive, I'm frankly quite peeved. I did everything right and now I'm getting punished with my computer essentially being neutered in regards to functionality ... because of a MS screw-up.
Not only is there the persistent watermark which overlays other programs and apps, effectively degrading the visual functionality of my screen, but certain base windows 11 functionality no longer works. I tried opening a word document (which I made on my old computer with office 2007) and it no longer runs the default word equivalent that comes with the OS.

The reasonable thing to do after this debacle would be to message all windows 11 users and offer them a temporary key (say 3 months or a 6 months).
As a legitimate customer, I shouldn't have to suffer as though I stole.

I have contacted my retailer who sold me the computer, (as I couldn't find the key on the case) so hopefully they will have it... but it's the weekend so they are off work and thus my weekend I will have a stupid watermark obscuring my screen.
This experience has me doubting the validity of leaving updates enabled, I gain nothing but pain... I don't need the bells and whistles just a computer that runs my games, and audio as well as giving me smooth access to the internet.

(I have tried all the above suggestions, I believe the update must literally wipe the Key Code from the computer thus the searches to pull it back give a null result)

HI I had exactly the same problem on a PC built for me by my local PC repairers. They suggested trying a scannow and then rebooting. I have just done this and lo and behold the deactivation watermark has gone. The system is still not activated though.

I have now found the activation key for the system and changed the key to that that had orignally been entered and I am now a happy bunny. It appears the 24H2 erased the original product key.

after the new update 24H2 my pc started showing an activate windows popup. when i tried to troubleshoot it said there was never a product code to begin with. i bought this computer about a year ago with windows 11 pre-installed. all i got sent was a disc and no activation code. if anyone can help please let me know.

Having the same issue with a build kit I bought from Corsair. Windows 11 was preinstalled by them. I've tried the cmd line prompt to retrieve the key with no results. I have currently rolled back to the previous update and the watermark is gone for now.