It is indeed strange to try to revert the screen locking. Normally people complain that the screen locks when they watch a video, e.g. in a browser.
In Gnome and KDE the screen locker or screensaver will not lock the screen if you watch a video in VLC or mpv etc and that makes sense. If you are not doing anything else it will.
Though you could disable some functionality in VLC, e.g. you can untick the box that disables the screensaver from the advanced options.
You could also disable all screensavers and screen lockers and use DPMS by setting it manually to always lock the screen at one specific time. That will work but is tedious to set up and will interfere with the desktop environment’s own settings, watching videos or doing presentations. It is more used by people that prefer window manager only setups.
There is a nice article on the Arch Wiki about DPMS settings.
https://wiki.archlinux.org/index.php/Display_Power_Management_Signaling