godv If fsck_msdos on GrapheneOS is crashing it is most likely because the file system on your removable device is corrupt and the specific corruption is triggering a bug. The code should not be crashing, so in the abstract it should be fixed, but that may not be as practical as fixing the file system corruption using a different computer.
A key issue is that the crash message you are receiving is not very detailed, so it is not enough information for a developer to find and fix the problem without also having your flash device. In theory, since you have your flash device, you could debug the problem and fix fsck_msdos. Alternatively, in theory you could mail your flash device to a developer who could use it to debug fsck_msdos. But neither of these options seems practical. That is the reasoning behind suggestions to fix the file system instead of fixing the version of fsck_msdos on GrapheneOS.
It is very unlikely that a fix to fsck_msdoswill happen as a result of the information provided so far, so waiting for a fix is not likely to be productive.