This is the correct link to download Sitecore 10.2.1 (rev 009559):
https://developers.sitecore.com/downloads/Sitecore_Experience_Platform/102/Sitecore_Experience_Platform_102_Update1
I just tried downloading one of the packages and can confirm it is correct.
Update 17/06/24
I think you are mistaken. There is no such thing as an update package (this was the old approach). You need to update your solution to use the new 10.2.1 DLL via nuget. Then follow the update guide T the link above.
Update 19/06/24
The Sitecore Nuget packages (including 10.2.1) are available via this feed: https://sitecore.myget.org/F/sc-packages/api/v3/index.json
See screen shot below:
All the information you need to upgrade from Sitecore 10.2.x to 10.2.1 is in the Update Installation Guide. One of the first sections shows this info:
To update to Sitecore XP 10.2.X, you must be a local administrator on
SQL Server and follow this methodology:
- Install the new version of Sitecore and any modules that you are using beside yourexisting Sitecore XP installation.
- Connect the new installation to your databases.
- Connect the new installation to your Solr indexes.
- Import the client languages.
- Deploy your solution on top of the new installation. • Perform the post-upgrade steps (optional).
Note that it says 'install new version beside existing'. This is the step that will provide the necessary config files (if any changed). You then deploy your newly updated solution (with 10.2.1 Nuget) over the top of the new sitecore.