CRT sclines emualtion.

Exactly CRT emulation - instead of a filter.

Black screen and then act like the Physically Works like in a CRT

Electron Gun Scanning:
    A CRT uses an electron beam guided by magnetic deflection coils to “paint” lines across the screen from left to right, top to bottom.
    When it reaches the end of a line, the beam is quickly moved back to the start of the next line (the “horizontal retrace”).

Odd Field:
    The beam starts at the top-left and paints only the odd-numbered lines down the screen.
    After finishing these lines, there is a short vertical retrace, and the beam is moved back to the top.

Even Field:
    Next, the beam paints the even-numbered lines between the previously painted odd lines.
    This completes the full frame.

Because these fields alternate so quickly, your eye sees them as one complete image with minimal flicker (in practice, some flicker can still be seen at lower field rates, which is why modern monitors use higher refresh rates or progressive scans).

In Summary:
When you see references to “double line” or “first line then second line” on a CRT, it describes how interlaced scanning draws two separate passes (fields) to build a complete frame—first odd-numbered lines, then even-numbered lines.

CRT vs Sharp looks

No file, test, or entry point is identified in the issue. Start by locating RetroArch's current filter or video-rendering path, then determine how a CRT-style implementation would represent scanning, retrace, and alternating odd and even fields. Done would mean a working CRT emulation mode rather than only a filter, with its visual behavior compared against the linked reference.