Krita 4.0.0 March 29 2018 STEPS TO REPRODUCE: 1) Krita can be in any idle state, with or without a file already active. 2) in the file menu, choose 'Open', 'Save As', or 'Export' options. 3) an empty dialog box appears where the file manager normally does, and Krita immediately crashes to desktop. I have never experienced this bug in any older version. After upgrading to 4.0 on March 29th, the bug was immediately present.
We had another Arch user on IRC yesterday who reported the same issue, but with more detail and a backtrace. For him at least the issue is a mismatch between the gtk library and the qt library used. He could work around this by disabling using the native file dialogs in Krita, so the GTK file dialog wasn't used anymore. You don't give any useful details like which desktop you're using, or a backtrace or anything at all, but it sounds very similar, and it's simply a bug in Arch's packages. Create a backtrace and report it whereever Arch wants bugs reported.
(In reply to Boudewijn Rempt from comment #1) > snip I found a thread on this bug on Reddit this morning; it must have been written by the same user mentioned. However, it was ENABLE Native Dialog that solved the problem for me. Disabling this option at any time brings the bug back. Sorry for lack of detail. I never wrote a bug report before, and I followed Bugzilla's instructions. Now I've found Krita's guidelines and will do better in the future.