Have a look at the changelog here:

https://helpcenter.websitex5.com/en/w5/changelog/preview

Yes, I know that, but this morning "updated" to version 2021.1.5, and it's not on this link!

The mentioned link already shows "WebSite X5 - 2021.2.1"!

Then what is true? 

2021.2.1 is a preview (beta) version.

Where can I download it?

https://helpcenter.websitex5.com/en/community/users/8710/preview_beta

Just be aware, if the real version comes out you can't use changes made with the preview version!

I'm sorry, I found it.

Why sorry? Have fun!

Give feedabck on items/problems, test the new features that's where the preview program is for.