If you have ruled out external causes such as malfunctioning media, or overhead caused by processes such as hard disk indexing, you may be suffering from a documented performance regression.
The issue typically manifests as unusually slow transfer rates, especially when copying or reading large numbers of small files. You may also experience stalling or the busy cursor when accessing your NTFS volume. In these cases we recommend older Macs running legacy versions of macOS (previously Mac OS X) be rolled back to version 2019 of our software (available here). For newer systems, especially ones running Apple Silicon (M1 or later), we recommend you upgrade to version 2021 or later.