SUMMARY
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Setting 'Tooltips On' causes a file name in the list to display a lot of file information in quite a big box. This covers much of the file list and makes it very hard to identify the file you want easily. It also duplicates what's in the information panel if that is also being used (I like it).
Bug ID   388583 looks to be the same but doesn't observe all the effects for the less educated user (like me) - I suffered many months of frustration before I worked out what was causing my weird file display.
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STEPS TO REPRODUCE
1. Go to Settings | Configure Dolphin | General | Behaviour | Miscellaneous
2. Click to set Show Tooltips and click OK
3. Go to any folder in Details View mode and highlight a file

OBSERVED RESULT
 A large information box appears with file information and properties and this normally obstructs a good portion of the file list, making it hard to select one file out of a list of similarly named files (e.g. lots of them and the selection having to be identified by looking carefully at the full filename).
This disrupted view can be eliminated by deselecting 'Show Tooltips' but then of course all the other (helpful and wanted) tooltips also disappear.
It was harder to rectify than you might expect because what appears does not look like a typical tooltip (I thought for a long time it was something to do with Previews, but it's not).  Nothing  in the Settings app indicates that each highlighted file will have a tooltip associated with it.

EXPECTED RESULT
I would not normally expect file information to be described as a tooltip and if it is desired to keep this feature then I suggest its presentation in the file list should be considerably streamlined, as much in the style of a typical tooltip as possible. 
It would also be helpful if the description in' Behaviour | Miscellaneous' could clarify that activating Show Tooltips will also impact on the display of file names.  I expect a tooltip to relate to a menu command or option or activation button, rather than to content displayed by the app. 
Dolphin already conveys very useful file information if the information Panel is activated and I don't see it makes much sense to duplicate that information in an overlarge tooltip.  Streamlining what's displayed might be all that's needed to make it usable though for me I'd be happy to see no tooltips for file names.
I think it could be solved by just removing file names from the items covered by tooltips, if that's easily achievable, but if not an info note that Show Tooltips affects filenames too would at least help the user to decide on what s/he wants to implement.


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Kernel 5.7.19.1 .Manjaro ARM (64 bit)
(available in About System)
KDE Plasma Version:  5.25.4
KDE Frameworks Version:  5.96.0
Qt Version:  5.15.5

ADDITIONAL INFORMATION
Hardware is Pinebook Pro