I've installed macOS mojave beta to test the dark theme, unfortunately keepass doesn't seem to fully apply the theming, resulting in a very bad look. Attached a screenshot presenting the issue

KeePassXC - 2.3.3
Operating system: macOS Mojave 10.14 Beta (18A314k)
CPU architecture: x86_64
Kernel: Darwin Kernel Version 18.0.0
This might be a Qt problem.
Yup, confirmed: https://bugreports.qt.io/browse/QTBUG-68891
Looks like rebuilding with the 10.14+ SDK will enable "most" of the colors to work as expected.
I think we will have to increase our minimum supported macOS version further or provide various builds for older versions in the future. Maintaining backwards-compatible macOS builds seems to be impossible.
Weak linking is apparently how you're supposed to do it. I think that means if you set the deployment SDK version to the older version, but set the target SDK version to 10.14 it'll enable the proper dark theme support while still supporting older versions of macOS. I don't have any experience developing in this area though, so that's just a guess.
ref: 2338
Duplicate of #2083 and #1931. Qt needs to release 5.12 which will support Mojave dark theme...
qt-5-12-lts-released. Excuse my ignorance in these matters, but is this dependant on the next release of keepassxc, or would I now need to install qt 5.12 on this mojave macos system?
Thanks in advance!
The next release will be built with 5.12
2.4.0 still looks pretty bad with Dark Theme. Is there a way to disable it for just KeePassXC?
URLs in the Preview pane are dark blue on gray.
The black group background is too stark against the group names/icons.
and When you have more than one DB open, the Selected tab text is black on dark gray.

I also saw the field content in an Edit window is white on white, but after I quit and restarted the app, it was OK.

These are all Qt bugs. I've already reported the tab coloring and it's been fixed in the next qt release.
Closing this issue as the remaining problems are not ours to fix at this point.
Most helpful comment
The next release will be built with 5.12