Git has a limit of 4096 characters for a filename, except on Windows when Git is compiled with msys. It uses an older version of the Windows API and there’s a limit of 260 characters for a filename.

So as far as I understand this, it’s a limitation of msys and not of Git. You can read the details here:
https://github.com/msysgit/git/pull/110

You can circumvent this by using another Git client on Windows or set core.longpaths to true as explained in other answers.

git config --system core.longpaths true

Git is build as a combination of scripts and compiled code. With the above change some of the scripts might fail. That’s the reason for core.longpaths not to be enabled by default.

The windows documentation at https://docs.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=cmd#enable-long-paths-in-windows-10-version-1607-and-later has some more information:

Starting in Windows 10, version 1607, MAX_PATH limitations have been
removed from common Win32 file and directory functions. However, you
must opt-in to the new behavior.

A registry key allows you to enable or disable the new long path
behavior. To enable long path behavior set the registry key at
HKLM\SYSTEM\CurrentControlSet\Control\FileSystem\LongPathsEnabled
(Type: REG_DWORD)