Created attachment 143879 [details]
screenshot

STEPS TO REPRODUCE
1. edit the /etc/fstab file to auto-mount a CIFS network share. The line of my CIFS network share in /etc/fstab looks like this:
//<ip-of-server>/share /mount/point cifs workgroup=workgroup,user,guest,iocharset=utf8,uid=myuser,gid=mygroup,noauto,x-systemd.automount,_netdev
2. turn on the client machine before the server and start Plasma session
3. turn the server machine on
4. open Dolphin in the client machine and click on your CIFS network share in Places panel, under 'Remote'

OBSERVED RESULT
Dolphin shows the inline error message seen in the attached screenshot:
"An error occurred while accessing 'mount/point', the system responded: mount error(16): Device or resouce busy. Refer to the mount.cifs(8) manual page (e.g. man mount.cifs) and kernel log messages (dmesg)."

Dmesg log says that Dolphin tries to mount the CIFS network share twice:
[ter nov 23 15:22:18 2021] CIFS: Attempting to mount \\<ip-of-server>\share
[ter nov 23 15:22:18 2021] CIFS: Attempting to mount \\<ip-of-server>\share

EXPECTED RESULT
Dolphin should mount the network share without any error message

SOFTWARE/OS VERSIONS
Operating System: KDE neon Unstable Edition
KDE Plasma Version: 5.23.80
KDE Frameworks Version: 5.89.0
Qt Version: 5.15.3
Graphics Platform: X11

ADDITIONAL INFORMATION
the observed result does not occur if I remove 'x-systemd.automount' mount option from fstab file