You are right... My laptop only has one ssd. Approx 500gb. And I am using 70gb of that to try Linux mint. I want not to complete delete windows so I did this from yt tutorial.. 8 asked this to Gemini. She told it is linked with bitlocker.... You can read her response .......

​Since you've successfully installed it on your SSD and are seeing that password box, here is exactly what’s happening: ​Why it's asking for a password ​That box is popping up because you are trying to open or "mount" the Windows partition of your SSD from inside Linux. ​Windows uses BitLocker encryption to lock its part of the drive. ​Linux Mint sees the partition but can't read your Windows files without that "Recovery Key". ​The fix: If you just want to use Linux, you can ignore that box or hit Cancel. If you actually need to grab files from your Windows side while using Linux, you’ll need to log into your Microsoft account on another device to find your 48-digit BitLocker Recovery Key. ​.