240p mode w CRT using Lakka and Pi 4 using composite cable?

I ask because I was able to set the 240p mode in config.txt using sdtv_mode=16 (For Progressive Scan NTSC), but when the menu came up it was as if it was still trying to render on a 480i screen, but since it was 240p the text was twice as large and only 1/4th of the screen was being shown.

Is there any way to tell Lakka/Retroarch to render everything at 240p?

Are you using the RGUI menu? It should scale down to 240p correctly.

The 240p mode over composite still appears as 480p to the operating system, IIRC. It just only shows half of the lines.