I have my work MacBook connected to a DisplayLink dock that runs three monitors, and I was experiencing a strange issue where KeePassXC would open on the middle (primary) monitor but be invisible unless I moved it to my left or right monitor.
After weeks of being annoyed by it (but not enough to look up a fix), thanks to r/KeePass it turns out it’s a really simple fix.
You just need to click “View > Allow Screen Capture”.