Thanks, tried now, mvim --clean, same results, the application crashes and does not respond until macos kills it.
It happens when the dragged tab overlaps the title bar.
Process: MacVim [28974]
Path: /Applications/MacVim.app/Contents/MacOS/MacVim
Identifier: org.vim.MacVim
Version: 9.1.0 (179)
Code Type: X86-64 (Native)
Parent Process: Vim [28973]
Responsible: Terminal [25289]
Date/Time: 2024-01-08 14:55:40.3414 +0100
OS Version: macOS 14.2.1 (23C71)
Report Version: 12
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x000042f2965f177e
Exception Codes: 0x0000000000000001, 0x000042f2965f177e
Termination Reason: Namespace SIGNAL, Code 11 Segmentation fault: 11
Terminating Process: exc handler [28974]