KeePassXC - 2.6.1
macOS High Sierra 10.13.6

Bug
When I start KeePassXC the DB login-screen is completely transparent. After selecting and logging into a database the symbol bar stays transparent. As soon as I resize the window the transparency vanishes and the black background for the symbol bar returns to normal.

Comment
I think its an OS Issue. On my macbook with the newest macOS Catalina everything works fine.
Unfortunately I can't update my desktop computer because of NVIDIA drivers that It need for motion & 3D stuff ;)

Screenshots
I attached some screenshots that show the problem. I used a blueish background so you can see where the transparency is visible... The transparency is also saved when I screenshot the programm window on macOS.

Cheers