Firmware D01-6C is the new firmware. Subsurface 5.0.10 is the latest release, which does not yet have the fixes to support this new Excursion firmware. Unfortunately there hasn't been a new subsurface release in a while, and you'll need to use a development build for now.
The link to the development builds was posted earlier (
Index of /downloads/test), but it looks like those builds have been removed now.
You can also try a build from the Github actions:
Actions · subsurface/subsurface
Choose one of the successful Pull Requests builds in the list (but not master), and there you can download a zip file with the Windows artifacts from that build. (Downloading the artifact does require a Github account.)