If you are not able to access a file share in samba / SMB externally, the selinux security system may need to be enabled to allow access.
Symptom: Mac cannot connect to an external share.
On the Linux box, you may see an error in /var/log/samba/log.smbd
[2021/07/31 21:36:31.620139, 0] ../../source3/smbd/service.c:798(make_connection_snum) make_connection_snum: canonicalize_connect_path failed for service bkup, path /mnt/8tb/backup
The solution as root or with sudo is to enable samba with selinux
setsebool -P samba_domain_controller on setsebool -P samba_export_all_ro on setsebool -P samba_export_all_rw on