We can confirm that Rainbow Six Siege does not support CPUs with less than 4 logical cores, which means Dual-core CPUs without Hyper Threading enabled are not supported. Here are the system requirements: https://support.ubi.com/en-GB/Faqs/000024358/PC-Requirements-for-Rainbow-Six-Siege
If you are above the minimum requirements and having technical issues, please create a support ticket[support.ubi.com] and attach your DXdiag/MSinfo[support.ubi.com].
- Ubisoft Support