Hi Richard,
You are right. Safe Mode does not accept a PIN because the TPM is not loaded, so Windows asks for your account password. The fastest way back to Normal Mode is to remove the Safe Boot flag from the boot loader using the Recovery Environment.
On the sign-in screen select the power icon, hold Shift, then click Restart. When the blue menu appears go to Troubleshoot > Advanced options > Command Prompt. In the Command Prompt window type this command and press Enter:
bcdedit /deletevalue {default} safeboot
If you get a message that the element was not found, run this instead and press Enter:
bcdedit /deletevalue {current} safeboot
Now type exit, choose Continue to Windows, and let the PC restart. It should boot normally again, and your PIN should also work.
If it still lands in Safe Mode after that, sign in and press Windows+R, type msconfig, press Enter, open the Boot tab, clear Safe boot, click OK, and restart.
Tell me how it goes or if you cannot reach the blue menu, I will give you an alternate way to open it.