Hello Malak B,
Thank you for your question.
The Bitlocker key is only requested by windows when it notices some kind of abnormal behavior of the system and that's why it asks for the key, for security reasons.
As you say it is asking every time, it may be that there is some kind of damaged file inducing windows to understand that there is something wrong with the system, in which case I would recommend Reset the PC. To do this just follow the instruction below:
Instructions: go to settings> update and security> recovery> reset your pc> select keep my files> local reinstallation and follow the step by step on the screen.
This should help eliminate this request every time you log in.
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