Once you’ve enabled BitLocker, you’ll need to enable the startup key requirement in Windows’ group policy.
To open the Group Policy Editor, press Windows+R on your keyboard, type “gpedit.msc” into the Run dialog, and press Enter. Head to Computer Configuration > Administrative Templates > Windows Components > BitLocker Drive Encryption > Operating System Drives in the Group Policy window.
Double-click the “Require Additional Authentication at startup” option in the right pane.
Select “Enabled” at the top of the window here. Then, click the box under “Configure TPM Startup Key” and select the “Require Startup Key With TPM” option. Click “OK” to save your changes.