How to log serial/USB port data into a text file in Linux?

hi

i used to have a really simple command to log all of the serial/USB port data into a text file, but now the whole internets is just filled with utter crap, so i cant find it from anywhere anymore...

it was something like this:
cat /dev/ttyUSB0 -> log.txt

but this now only gives an error:
cat: /dev/ttyUSB0: No such file or directory

and i wonder if i actually had to use the pure Uart mode somehow in Linux and how can i do that, lol (with somekind of special adapter?)

What do you see if you do a

stty -F /dev/ttyUSB0