SUMMARY
During a running session, a USB stick can only be mounted once. When it is sticked in for the second time, there is no notification in 'devices' notifier, it is not even shown.

Successful 1st attempt:
Sep 19 14:07:53 X1E kernel: usb 1-1: new high-speed USB device number 10 using xhci_hcd
Sep 19 14:07:53 X1E kernel: usb 1-1: New USB device found, idVendor=8644, idProduct=8005, bcdDevice= 1.00
Sep 19 14:07:53 X1E kernel: usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
Sep 19 14:07:53 X1E kernel: usb 1-1: Product: USB Flash Disk                
Sep 19 14:07:53 X1E kernel: usb 1-1: Manufacturer: General                       
Sep 19 14:07:53 X1E kernel: usb 1-1: SerialNumber: 0475020000001F9A
Sep 19 14:07:53 X1E kernel: usb-storage 1-1:1.0: USB Mass Storage device detected
Sep 19 14:07:53 X1E kernel: scsi host1: usb-storage 1-1:1.0
Sep 19 14:07:53 X1E mtp-probe[22641]: checking bus 1, device 10: "/sys/devices/pci0000:00/0000:00:14.0/usb1/1-1"
Sep 19 14:07:53 X1E mtp-probe[22641]: bus: 1, device: 10 was not an MTP device
Sep 19 14:07:54 X1E mtp-probe[22679]: checking bus 1, device 10: "/sys/devices/pci0000:00/0000:00:14.0/usb1/1-1"
Sep 19 14:07:54 X1E mtp-probe[22679]: bus: 1, device: 10 was not an MTP device
Sep 19 14:07:54 X1E kernel: scsi 1:0:0:0: Direct-Access     General  USB Flash Disk   1.00 PQ: 0 ANSI: 2
Sep 19 14:07:54 X1E kernel: sd 1:0:0:0: Attached scsi generic sg0 type 0
Sep 19 14:07:54 X1E kernel: sd 1:0:0:0: [sdb] 15669248 512-byte logical blocks: (8.02 GB/7.47 GiB)
Sep 19 14:07:54 X1E kernel: sd 1:0:0:0: [sdb] Write Protect is off
Sep 19 14:07:54 X1E kernel: sd 1:0:0:0: [sdb] Mode Sense: 03 00 00 00
Sep 19 14:07:54 X1E kernel: sd 1:0:0:0: [sdb] No Caching mode page found
Sep 19 14:07:54 X1E kernel: sd 1:0:0:0: [sdb] Assuming drive cache: write through
Sep 19 14:07:54 X1E kernel:  sdb: sdb1
Sep 19 14:07:54 X1E kernel: sd 1:0:0:0: [sdb] Attached SCSI removable disk
Sep 19 14:07:54 X1E dbus-daemon[1266]: [system] Activating service name='org.kde.kded.smart' requested by ':1.175' (uid=1001 pid=17156 comm="/usr/bin/kded5 ") (using servicehelper)
Sep 19 14:07:54 X1E dbus-daemon[1266]: [system] Successfully activated service 'org.kde.kded.smart'
Sep 19 14:07:57 X1E udisksd[2315]: Mounted /dev/sdb1 at /run/media/docb/OPENSUSE on behalf of uid 1001
Sep 19 14:07:57 X1E systemd[17004]: Started kde-open5.
Sep 19 14:07:57 X1E kde-open5[22709]: kf.service.services: KApplicationTrader: mimeType "x-scheme-handler/file" not found
Sep 19 14:07:57 X1E systemd[17004]: Started Dolphin - Dateiverwaltung.


Stick is unmounted afterwards, physically removed from slot and plugged in again:
Log entry is basically the same, EXCEPT that last entry is the line:
Sep 19 14:08:26 X1E dbus-daemon[1266]: [system] Successfully activated service 'org.kde.kded.smart'

-> no automatic mount or display in device notifier

Operating System: openSUSE Tumbleweed 20210916
KDE Plasma Version: 5.22.5
KDE Frameworks Version: 5.86.0
Qt Version: 5.15.2