Samba + exFAT : how to avoid pre-allocating when copying big files?

[Joseph]

Hello,
When sending a big file (for example 2 GB) from a Windows computer to a
Linux computer (with Samba server), then:
* if the destination FS is ext4, NTFS, no problem
* if the destination FS is exfat, then there is a strange delay (~30
seconds) during which the Windows Explorer waits, before actually copying
the file
It seems that the Samba server first "preallocates" the 2GB, before
accepting to start the copy from Samba client.
Thus, 2GB (of probably null bytes?) are first written, and then, the
actual file is written.
How to avoid this effect that doubles the number of gigabytes written and
doubles the transfer time?

I have already tried:

    strict allocate = no

without any success in the exfat case.

Any idea?

PS:
* I've already tried exfat-fuse, but also exfat-nofuse, and also exfat (non
fuse) included in Kernel 5.7, and it's the same.
* There are many forums posts with the same problem, e.g.
https://www.raspberrypi.org/forums/viewtopic.php?t=206866

Thanks,
Jo