In windows start regedit as administrator and navigate to/create HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome.

Under the Chrome key, create a DWORD value named "ExtensionManifestV2Availability" with hex value 2.

Restart Chrome. If successful, you'll notice the ExtensionManifestV2Availability entry with value 2 in chrome://policy and the settings page will mention "managed by your organization".

If I recall correctly only till June 2025, did they change the date?

I'm not sure but a lot of people hypothesize that they will have to keep this feature for enterprise customers (not for UBO but other custom enterprise extensions that use manifest v2)

they can easily just blacklist ubo if they really wanted to remove it. And they can make it plausibly deniable - by blacklisting the extension id of anything that is in the chrome extension store that originally had manifestV2 (which will have some collateral damage, but obviously google doesn't care).

But that would also harm companies that actually intend to switch to a v3 based replacement but need a bit of time to complete the development.

That's what the registry entry for the manifestV2 time extension is for - this was actually known for several years already, and 2025 june is meant to have been the deadline for that development.