Hi GreenBulba,
We're sorry for the delayed response.
On-screen keyboard is basically different from Touch Keyboard and the OSK can only be activated within the Windows environment. If outside the Windows environment, like when it is starting up and you have to enter the bitlocker key or the TPM pin, you might need to utilize the physical keyboard for that. Well, in your case, I have to try it on a Surface device to confirm if touch keyboard will work in the pre-boot environment. After I'm done testing few devices, I'll get back to you to give you some updates.
Kind Regards,
Crest