SUMMARY

So.  I got yet one more another HDD, just in case.  [[ but actually it's not in case, it's a standalone 2.5" portable type, and it needs an external case and a connector. /jk ]]

So i plugged it in.  It's all clean and wiped, there's no data at all.  Naturally, OS doesn't know what to do with it; and KDE in particular didn't suggest anything either.  It's not in Disks & Devices applet, nor in Dolphin sidebar.  There's ABSOLUTE NO UI that says "hey, I see you plugged in an empty disk.  you need to format it in order to use.  wanna do it now? [Format] [Cancel]"

STEPS TO REPRODUCE
1. Buy a new storage device, or wipe with zeroes an existing one. [[USB sticks often come pre-formatted with FAT32, while HDDs are usually left blank]]
2. Connect to a computer with running Plasma session.

OBSERVED RESULT
No UI for formatting this disk at all. You'd have to manually open KDE Partition Manager and choose this particular device in the list of devices there.

EXPECTED RESULT
Plasma should offer "Format" action for an empty device somewhere. We already have "Disks & Devices" applet in system tray which does that for mountable (i.e. already formatted) partitions — which isn't tremendously useful when you don't even have a partition table to start with.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: git-master
Qt Version: 5.15.8
Kernel Version: 6.1.9-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-6700HQ CPU @ 2.60GHz
Memory: 15.6 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 970M/PCIe/SSE2
Manufacturer: ASUSTeK COMPUTER INC.
Product Name: G752VT
System Version: 1.0