Mac mini: File Attachment Window Opens as a Large White Horizontal Block and Cannot Be Resized Properly

[u/nerdangel94]

I’m experiencing a strange issue with Apple Mail on my Mac mini.

Whenever I compose a new email and click the attachment button, the file selection window opens as an extremely wide, blank white horizontal block. The window extends beyond the screen boundaries, making it impossible to access the files or select an attachment.

I can resize the window vertically, but not horizontally. Changing its height doesn’t resolve the issue or reveal the missing content. The white block also moves together with the Mail compose window.

Tried safe mode, upgraded from Tahoe to Golden gate, reinstalled the macOS l, changed resolution the issue still persists.

The Mac mini is connected to a single external monitor.

Has anyone experienced a similar issue with macOS

[u/TrackerDesk]

Quick workaround while you fix it: drag the file from Finder straight onto the compose window, that skips the broken panel entirely. The open panel remembers its size per app, so quit Mail, run defaults delete com.apple.mail NSNavPanelExpandedSizeForOpenMode in Terminal, and reopen it. If Terminal says that key doesn't exist, clearing Mail's Saved Application State folder inside ~/Library/Containers/com.apple.mail is the next thing I'd try. A full reinstall not fixing it is actually good news, it points at a prefs file and not your Mac.