Qt's file dialogue is partially broken under Linux

Qt's file dialogue is partially broken under Linux. It has the following issues:

1. Cannot adjust column width.
When I hover my cursor over the edge of a column header, the cursor doesn't its icon, and thus I cannot drag to adjust the width of a column. To work around this, I have to adjust the size of the dialogue.

2. Cannot sort files by clicking on column header.
The column header is not clickable. I cannot sort files because of this. However, the column can be clicked SOMETIMES. I haven't figured out its pattern. I mitigated this issue ONCE, by restarting the system. When I was writing this report, I was unable to make it work.

3. It doesn't remember the location or file type I used last time.

4. It doesn't remember the hidden state of thumbnail.

5. It doesn't remember the dialogue size.

All these issues make saving many files a real chore.

Tested with Krita, Kdenlive, digiKam, ArchLinux native packages and project official appimages. I marked the affected version as Qt 5.15.4, but it should go much earlier, because Krita's appimage was built with an older Qt version, digiKam's appimage used an even older Qt, then Kdenlive used the oldest of them all. All of them have the same broken Qt dialogue.