Maybe related to this issue : 1903955 – cannot connect to samba NT1 share with gvfs
Downgading samba and smbclient to 4.13.5 fix the problem for me. (was 4.14.2)
pacman -U https://archive.archlinux.org/packages/s/samba/samba-4.13.5-1-x86_64.pkg.tar.zst
pacman -U https://archive.archlinux.org/packages/s/smbclient/smbclient-4.13.5-1-x86_64.pkg.tar.zst