How actually I can install add-on in Plone 6 backend

Plone Support Customizing Plone
1

I have create a test based on
Install Plone with Cookieplone Install Plone with Cookieplone — Plone Documentation v6

Every work fine out of the box.

My question is how can I install add-on in backend?

I do follow this Install Plone add-ons — Plone Documentation v6

But no success, anyone please point me a doc that actually work?

Many thanks

2

What steps did you do, and in what way did it fail to work? We can't read your mind. The doc you linked represents our best effort to provide usable docs for this, but there are many different factors and many different reasons things can go wrong.