Hi BeastNae,
Welcome to Microsoft Community.
It may be an expected situation for the decryption process to take a long time and affect the performance of the drive.
Depending on the size of the drive and the encryption method, it can take hours or even days to decrypt a drive.
During the time, you may experience slow read and write speeds, or even errors when trying to access the drive.
The decryption process may need to read every bit of data on the drive and decrypt it before writing it back to the drive. Device encryption is implemented based on BitLocker.
BitLocker overview - Windows Security | Microsoft Learn
BitLocker can use different encryption methods for each type of drive, such as AES-CBC, XTS-AES, or hardware encryption.
Setting the BitLocker encryption algorithm for Autopilot devices | Microsoft Learn
The Answer community is primarily involved in general guidance at the usage level for products that do not involve complex device environments or complex networks.
The issue on BitLocker and Device Encryption is out of reach of the response support community.
For further professional assistance, it is more suitable for publishing on Microsoft Learn (English only), you can click on "Ask a question", there are experts who can provide more professional insights in that place. Here is a link to the forum where you can raise specific scenarios and share your idea to help analyze the problem. Windows 11 - Microsoft Q&A
I won't be able to provide a precise interpretation of the technical aspects, but I'll leave that question open in case one of our amazing volunteers has ideas for you.
Thanks for your patience and cooperation!
Best Regards,
Kyo - MSFT | Microsoft Community Technical Support