If I am trying to open a file that is not a part of any project, and I don't have any other projects loaded, qds tries to open the file in Design Mode and instantly crashes.

Looks like crash happens when it tries to instantiate design view (currently it occurred in ConnectionManager), when it calls Puppetcreator.cpp::createQml2PuppetExecutableIfMissing(), where it reaches line else if (m_target->kit()->isValid()), where m_target is nullptr.

My build has default kit with qt5.15, however for the testing purposes I am using file that is not part of a project, so I guess it doesn't have a target.

Crash currently occurs on 5.0 branch (so it may get in qtc5.0-rc and qds2.2-beta).