Hello! My name is Renzo and welcome to Microsoft Community.
It seems like the change in the Windows version to "Windows 11 Pro" after reactivation may have been triggered by the hardware changes (the motherboard update and TPM/security module activation). Microsoft often considers significant hardware changes as a reason to prompt reactivation of Windows.
Since you originally activated Windows 10 Pro for Workstations and then upgraded to Windows 11 Pro Workstations with a digital license, this should still be valid as long as the product key is properly linked to your Microsoft account.
The discrepancy in the product key and the version change might be due to the reactivation process, where it reassigned the system to a different version (Windows 11 Pro instead of Windows 11 Pro Workstations) after the hardware change. However, the fact that it still shows "Windows 11 Professional Workstation" in your Microsoft account suggests that the digital license is still recognized.
It doesn’t seem like you need to reinstall or repurchase, but you may need to check the activation status of your device.
Go to Settings > Update & Security > Activation to confirm whether your system is activated.
If it is activated and it shows on your Microsoft Account too, I don't think there is a need for reinstall or repurchase but if you prefer to have Windows 11 Pro Workstation, you may reach out to https://support.microsoft.com/en-us/home/contac...
I hope this answer your inquiry. In case of additional questions, reach out back to me, and I will be happy to help and try my best to resolve your issue. Thank you.