You request to know if there are any limits to the number of items in the Allow/Deny lists in the Symantec Protection Engine (SPE).
SPE 9.x0
There is no known limit to the number of file name/extensions or files hashes (SHA256) that can be added to the Allow or Deny list in SPE. While there is no known limit to the number of items in the Allow or Deny list, enabling file hash (SHA256) based exclusions may impact performance due to the cost of calculating SHA256 values.
There is a limited number of file true types supported by SPE for file type filtering. For a full list of the supported true types, please see Supported file types for true type file filtering in SPE.