SUMMARY

Creating new folder on sftp:// server from Save File dialog crashed the whole thing. Sublime Text, which initiated the dialog, survived the crash though, and continued to run as nothing happened.

Backtrace: https://invent.kde.org/-/snippets/2041

STEPS TO REPRODUCE
1. Create new file in any editor that can use xdg-portal, e.g. Sublime Text or Kate.
2. Hit Save or Save as…
3. Navigate to an sftp:// server, if you got one. I don't know if this is sftp-specific -- maybe other special locations:// would work too.
4. Select «New Folder» action (there's a button on the right of a toolbar, and it's in a context menu too)
5. Enter a valid folder name, and confirm (OK/Enter)

OBSERVED RESULT

Portal dialog crashes. Although the folder was already there the next time I opened the dialog.

EXPECTED RESULT

Should not crash.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.23.80
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2
Kernel Version: 5.15.12-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

ADDITIONAL INFORMATION

It is not consistent. There might be some race condition, or network lag affecting the bug.