There are two versions of Bitlocker
Encryption - this is a cut down version of full Bilocker as below.
This works at the device level and all
drives/partitions with letters are Bitlocked.
This is available on Home and Pro for qualifying pcs.
To qualify PC must have a TPM, Modern Standby, and you must use an MS Account (as that is where the Recovery Keys are stored)
Form a security viewpoint, the PC is only as secure as the Windows Password/PIN. The drives automatically open upon logging in.
However, if a thief could not get past that (strong passwords are essential), they can remove the drive(s) to try to read them on other device - this is where the encryption comes in - they cannot read the drives.
The key point is this encryption mode is "all drives or no drives".
Encryption - this is the full version available on Pro.
This works at the drive level rather than the Device level, and user has a lot more flexibility e.g. you can bitlock one drive independently of the others.
You can add passwords for each drive etc. This will work on any pc - it can be hardware locked if a TPM, or software locked if an older device.
Perhaps the most important additional security feature is the ability to add a Bitlocker PIN - pc will not boot if this PIN is set (it is a separate PIN to Windows login PIN). However, you should still have a strong Windows Password/PIN.
In time, it is likely virtually all (new) laptops will be Bitlocker Device
Encryption capable but desktops will vary somewhat as Modern Standby is less common on desktops.