Is there anyone who can offer me a way to get there?
I think you can still buy RGB (analog) to Composite Video encoder chips.
That manages all the Analog/phase stuff and you just need to feed it information.
There are still available parallel DAC, like ADV7123, that are an overkill, but simple to apply.
In 2024 a simple way to manage that would be a sprinkle of fast SPI Serial SRAM, Microchip now make 4MBit SRAM, so you might allocate one for each of R,G,B,Sync.
- you then fill the RAM from FLASH with any pattern you like, and play back.
With a bit more SW effort, you could look at a part like Parallax P2.
That has Video DACs and high speed IO, that could probably swallow everything into a single part.
eg
https://forums.parallax.com/discussion/173102/ntsc-pal-driver-without-dot-crawl-new-version/p1