When I thought about the idea of starting ports for the Original Xbox, I had (and still have) the desire to port the decompilation of Sonic Mania (RSDKv5), but I saw that this would require an experience in ports that I don't have (yet).
So I decided to go in baby steps, to gain experience, so I studied and made my first port for the Xbox, Celeste Classic (https://github.com/danielgpinheiro/ccleste-xbox)
After this port done, where I learned a lot, I'm starting a series of Retro Engine ports, which will start from version 1 (which runs Sonic Nexus), next version 3 (Sonic CD 2011), version 4 (Sonic 1 and 2 2013), and version 5 (which runs Sonic Mania).
The first port of this series is complete, which is the RSDKv1 for the Xbox, which runs the Sonic Nexus fan game. Who is interested, the link to the repository: https://github.com/danielgpinheiro/RSDKv1-xbox