And you say in your original post you tried, the solution here and it worked for the classic notebook.
Did you try the following variations for JupyterLab?
python -m jupyterlab
python -m lab
python -m jupyter-lab
python -m jupyter lab
The comment there by Georgy has the first one but I thought maybe another typo and so was worth trying some variations?
Did you search that issue and try any of the solutions? Such as: