Created attachment 132000 [details]
View of Dolphin after the window has been shrunk.

SUMMARY
Noticed after messing with https://bugs.kde.org/show_bug.cgi?id=427100

After the error dialog pops up, when shrinking the window the panels on the left side get shrunk instead. (normally it would stay the same width whilst the inner panel shrinks).
After this, the window can no longer be resized any smaller than the width of the text in the error message.

STEPS TO REPRODUCE
1. Resize window to a size greater than the length of the error message on one line (maximised works here, anything smaller allows the text to resize properly).
2. Press an unmounted volume, then hit cancel
3. Try to resize the window smaller than the error message box.

OBSERVED RESULT
The places panel on the left shrinks until it is about ~20px wide, whilst the inner (middle) section does not. Resizing gradually will gradually shrink the "places" panel under it meets a minimum width and you cannot resize the window further. 

Also, using window snapping to resize width to smaller than the the minimum window width creates an issue where the information panel on the right disappear and the error message + folder pane extends outside the panel borders.

EXPECTED RESULT
The places panel remains the same size and the error message flows to fit the centre box.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.19.90
KDE Frameworks Version: 5.74.0
Qt Version: 5.15.1
Kernel Version: 5.8.12-arch1-1
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-6500 CPU @ 3.20GHz
Memory: 7.6 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 530

ADDITIONAL INFORMATION