It is just 30 and not 5.30 (the naming has changed from Version 5.27.2 to 29, see changelog)
new version is 29. the 28 was 5.27. the 1st (with the same technical arch) was 5.0.
https://batocera.org/changelog
For your issue just go to System Settings, Developer, Format A Drive and format your drive there and reboot. After that you will be able to use the full capacity of your drive. In the next version (31) this issue will be fixed, so that you do not have to use this workaround method anymore.