IMPORTANT UPDATE: The issue with uploads of size greater than 1 mb failing silently in ways that made data seem gone has been addressed as of March 29, 2023 if you use JupyterLite version 0.1.0b22 and beyond. “The effective ceiling is now much closer to some of the limitations of the browser, with files up to 50mb.”
I am wondering if you might be running into this?
You’ll note in the post I referenced the person clearly described what type of situation they have for Jupyter. You didn’t do that in your post above. There’s a lot of ways to use Jupyter while working online, which is all the information you provided in your first paragraph. For example you could spin up a super large cloud computing system from one of the many commercial suppliers and install JupyterLab there and then log into that from your local machine.
If you are using JupyterLite, I suggest you’d have an easier time using a typical, full python kernel online, and not the Pyodide-based one. I detail here how you can use a temporary system served via the MyBinder service to achieve that.