Dear @kitaniabdellah,
It seems to me that your problem installing flair are related to some issues with your linux ubuntu installation. Looking better at the last screenshot you sent I understand that somehow ubuntu isn’t able to replace some damaged package.
Unfortunately for you, solving generic ubuntu related problems is beyond the scope of this forum. I suggest you to look for help on an ubuntu dedicated forum/website first, and only then to try again installing Fluka, possible from a clean system.
Good luck.
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Thank you sir for your help