Reality Engine 4.25 adds support for long file paths for cook name for users with Windows 10 Anniversary Update! Historically, paths in windows have been limited to 260 characters, which can cause problems for projects with complex naming conventions and deep hierarchies of assets. The Windows 10 Anniversary Update adds support for much longer filenames, on the condition that the user and each application opt-in to it.

To enable long file paths in Windows 10: Ensure you're running Windows 10 version 1607 or later.

Enable support for long paths via the group policy setting or registry, see:

Setting Enable Long Paths Support in Unreal Engine.

Go to the Edit menu and from the Configuration section, select “Editor Preference”.

Go to General > Experimental > Content Browser section and tick the option “Enable support for long paths”.

Or simply type in Search Details, "long" as shown below and you can find the option instantly without scrolling through the sections.

Support for long paths is not universal, and third-party tools - even parts of the operating system, like Windows Explorer - may not support them correctly.