Permissions for new files omit group write permission

Using the Dropbox Sync app on a Linux machine

Newly created files lack the "Write" bit and this makes the shared folder inaccessible for other users on the network.
Already checked the `umask` and it is correctly set to 0007 for the user, and also for the process when queried using `gdb`
Running `strace` on the file writer thread I see the following:

openat(AT_FDCWD, "/mnt/Dropbox/.dropbox.cache/new_files", O_RDONLY|O_NONBLOCK|O_DIRECTORY) = 120
fcntl(120, F_SETFL, O_RDONLY)           = 0
fstat(120, {st_mode=S_IFDIR|0770, st_size=7, ...}) = 0
mkdirat(120, "18075a7c044f08a6659c56dd00da82ed", 0755) = 0
openat(120, "18075a7c044f08a6659c56dd00da82ed", O_RDONLY|O_NONBLOCK|O_NOFOLLOW|O_DIRECTORY) = 121
fcntl(121, F_SETFL, O_RDONLY)           = 0
fstat(121, {st_mode=S_IFDIR|0750, st_size=2, ...}) = 0

...

openat(AT_FDCWD, "/mnt/Dropbox/.dropbox.cache/new_files", O_RDONLY|O_NONBLOCK|O_DIRECTORY) = 58
openat(58, "18075a7c044f08a6659c56dd00da82ed", O_RDONLY|O_NONBLOCK|O_NOFOLLOW) = 105
fcntl(105, F_SETFL, O_RDONLY)           = 0
fstat(105, {st_mode=S_IFDIR|0750, st_size=2, ...}) = 0
fstat(58, {st_mode=S_IFDIR|0770, st_size=8, ...}) = 0
fstat(123, {st_mode=S_IFDIR|0750, st_size=3, ...}) = 0
newfstatat(123, "Test2345", 0x7f8976bf6d80, AT_SYMLINK_NOFOLLOW) = -1 ENOENT (No such file or directory)
renameat2(58, "18075a7c044f08a6659c56dd00da82ed", 123, "Test2345", RENAME_NOREPLACE) = -1 EINVAL (Invalid argument)
newfstatat(123, "Test2345", 0x7f8976bf6be0, AT_SYMLINK_NOFOLLOW) = -1 ENOENT (No such file or directory)
renameat(58, "18075a7c044f08a6659c56dd00da82ed", 123, "Test2345") = 0
utimensat(123, "Test2345", [UTIME_OMIT, {tv_sec=1673373843, tv_nsec=0} /* 2023-01-10T19:04:03+0100 */], AT_SYMLINK_NOFOLLOW) = 0
newfstatat(123, "Test2345", {st_mode=S_IFDIR|0750, st_size=2, ...}, AT_SYMLINK_NOFOLLOW) = 0
close(105)                              = 0

So the directory is created without the group write bit

Is this hard-coded? How can this behaviour be changed?