Annotation:
The developer offers a 50% discount on any template you have already bought in the Joomla 3 version. You must enter the discount code before purchasing. Every Joomla 4 template has to be bought new. The edits for Joomla 4 are big...

(I can't say why you already have the Everly for J4... )

Thanks for the explanation.
Where can I read this news? Where can I get my discount code?

And of course somebody deleted my Evelry J4 version without further notice. (I don't think the system heals itself...) I don't care about to buy the J4 version again - but a small mail to explain the availability error of Everly J4 as a mistake and that it's now deleted would be nice...
Information is power, that's why google grew so big... but I miss a lot of information here...

Joomla51 needs a news page or a blog to post central information - a forum isn't useful.
Even if I have to contact support for my discount code, ok - but where do I get the information that this is the way?

When choosing your template, which you have already used in J3, make sure that you click on the J4 version and then buy it. You can then enter the code (under coupon) in the "shopping cart".
Here are the codes announced by the developer:

https://www.joomla51.com/forum/individual-purchases-of-3-xx-template-upgrade-to-joomla-4-xx