An Xbox Series X / S user could find a way to expand storage by using a consumer SSD PCIe Gen4 and not a console-proprietary Seagate. The user used an NVME to CFexpress converter, and there appear to be no compatibility problems. This is not a permanent workaround, but further testing will be needed first.
As you know, the Xbox Series X / S SSD card slot can be expanded using only Seagate expansion cards thanks to a partnership with Microsoft. Therefore, Xbox users cannot use third-party SSDs, but a certain Bilibili may have found an alternative way to expand the storage.
As reported on VGC and its blog, the user connected a consumer PCIe Gen4 SSD to his Xbox Series using an NVME to CFexpress converter. The SSD used for the mod was a Western Digital SN530 m.2 2230, which Microsoft uses inside its consoles. This would explain why the SSD was recognized without problems, but it is still unclear whether other SSDs are also compatible or not.
There are also no details on how this solution can last over time, so it is obvious that still more tests are needed to understand what to do. Although unofficial, this seems to be the only expansion alternative to Seagate’s SSDs, at least until Microsoft announces something about it.