After playing with preview for the last week I can say this is not a Joomla issue :-)

I cannot replicate this at all, in any environment

The error actually says that your browser could not connect to the server... maybe your server was having a down moment?

@micker check that your apache has the right mimes.types enabled, eg https://github.com/joomla/joomla-cms/files/6725305/mime.types.txt

@micker could you resolve it following the link of @dgrammatiko? If yes, then please close this issue.

sorry i didn't receive notificati
systeminfo-2021-09-17T13_46_57+02_00.txt
on

@micker can you share the file that is not getting a preview?
Did you read my other comment? Does your mime.types file allow all the extensions needed for Media Manager to function properly?

sorry @dgrammatiko i thinked all information are in system export file
can you explain wjere i can find this information ?

i found an error in console log
Refused to display 'https://www.....com/' in a frame because it set 'X-Frame-Options' to 'sameorigin'.

make sure you are visiting your website with www in the domain name then...

Also make sure you have NOT set $live_site value in /configuration.php

@micker sorry I misread the issue, your problem is the missing icon in the preview button in the toolbar (assuming in the article edit view). I can't recreate the issue. Would help to share the inspected element like:

hello
about icon that flase bug => a plugin conflict
about preview, nothing in livesite but yes @dgrammatiko with www all works ... bug ? or config serveur problem ?

i found thanks @dgrammatiko to help to find it, a plugin conflict with www redirection plugin