While that is an option, that wasn’t what I was suggesting for now. You can follow what I pointed out above to use a typical, full Python kernel on a temporary remote machine. As I suggested above you can follow the instructions here to use sessions served by MyBinder.org to have typical, full Python kernels in JupyterLab in your browser without installing anything and not requiring login. If the behaviour is different there and it works without cutting off anything in your CSV file than you know it is JupyterLite/pyodide/browser-limitations in play as the culprit.
I think I missed in the original version of my last post that you posted a view of the uploaded CSV already:
While that isn’t looking directly at the lines of text in the Editor view, I suspect it does indicate the file upload process got cut off in some way as if it was too large to be completely uploaded. In other words, you are having the trouble I specifically suggested in my first reply.