@Isaac
As suggested by trent, the maximum size of a Storage Spaces Direct (S2D) share folder is 64 TB. If your share folder is already 64 TB and almost full, you cannot expand it to a larger size. Instead, you will need to create a new share folder and move some of the data from the existing share folder to the new one.
After the new share folder is created, you can move some of the data from the existing share folder to the new one. You can use tools like Robocopy or PowerShell to copy the data while preserving the file permissions and attributes.
Keep in mind that creating a new share folder will require additional storage space and may affect the performance of the storage pool. It's recommended to monitor the storage pool and adjust the virtual disk and share folder settings as needed.