The presumption for much of the interface of LibreOffice (and many other programs) is to pick up the operating system’s (and user’s selected) features so it appears as an app designed for that interface.
The bug report to implement the dark theme is Bug 118320 - Add support for Windows 10/11 dark mode
You can see where it is implemented in 7.4.3. It looks as if the intention is to make it switchable between system and user selection but that might not be implemented yet. There is an all-encompassing report, Bug 150915 (Windows-Dark-Mode) - [META] Windows Dark Mode bugs and enhancements
You could revert to LO 7.3 (stable) and see if LO 7.5 when it is released has a control to turn off dark mode in LO; I can’t find one in LO 7.5 beta
One thing that should be remembered is that Dark Mode isn’t perfect in Windows, I find that if I switch between modes the Windows Taskbar gets out of synch and becomes black in light mode and dark in light mode until rebooted.