Of Course Rockets Can't Work In A Vacuum
Scale and proportion matter. This is not an example of a rocket in a vacuum; this is obviously an example of a rocket in a gas filled tube.
"I Ignited a Model Rocket Engine inside a giant vacuum chamber i build to see whether or not it will burn while filming it in 4k slow motion. the idea here is to replicate how rocket engines and Rocket motors burn in space in a vacuum where there is no air." source: Youtube - Model Rocket Engine In A Vacuum Chamber - 4K Slow Motion...
Consider subatomic sized rocket compared to the vastness of the supposed vacuum of outer space.