I can't remember since when i'm using opera, because it's my main browser for years.
I really love this browser but damn, this deleting was really annoying.
Thx you so much to people for providing the solution :
- opera://flags/#search-in-open-tabs => from Default to Disable
Improved search in open tabs
Improvements in the Search in Open Tabs feature. – Mac, Windows, Linux
Opera will stay my browser until they remove definitly this Tab button.