No module named 'apt_pkg'

[stevef]

You can have different versions of python in parallel on your system, but if the system default is changed it is likely to cause problems.

The worrying bit in the instructions you linked to is

.... and configure it as the default version of Python in Ubuntu 20.04 and 22.04 LTS.

This should come with a warning really.
The comments under the instructions show that others also had problems after following the instructions.

I want to believe I used the right way

It was necessary to reverse whatever was done to change the system default - so step 4 of the instruction needed to be undone which you did.