OK. So riffing off what you're saying, IF this works, & that's a big if, it might work, it might not . . .
So, IF it works, it would look something like this:
yt-dlp -f whatever -o "1st target file name" "1st master manifest URL" -o "2nd target file name" "2nd master manifest URL"
Is -f a parameter that applies to the execution of the command or does it need to be repeated as well for each download? That means the command might be this:
yt-dlp -f whatever -o "1st target file name" "1st master manifest URL"
-f whatever
-o "2nd target file name" "2nd master manifest URL"
If this works . . . IF . . . it looks like you could invoke as many downloads in one command as you like. There might be a maximum. I would rely on the documentation to tell me that maximum.
I have to say that given the messages our pal Ben posted, it looks like yt-dlp was at least trying to do the second download. It also looks like it was choosing some sort of default file name for the first download. I've mentioned before that I hate defaults. Here's a case in which relying on defaults will likely not work. Don't rely on a default for the target file name on ANY of the downloads you might try in a single invocation of yt-dlp.
But it appears that the downloads are executed one after the other. Personally, in my usage of ffmpeg, I do single downloads but I do multiple commands in separate command windows. That way I can get multiple concurrent downloads going. It works great. The headache is making sure all the file names across all the command windows are unique. This is why I rely on both the standard Windows command language as well as a scripting language known by the name REXX. I will not elaborate on REXX. It's way off topic here & I think we're already pretty far off topic. Coming back to yt-dlp, you want to go back to a single download per command, but proliferate commands in separate command windows to your heart's content. Just pay attention to making all the file names unique across all sessions.