I have lunch now. Are you there later? I would try to solve the problems later.
It looks like we are in the same time zone 
bon appétit !
I'm back. Yeah. I'm living in Germany and you seem to live in France, right?
I think i will really have to reinstall Linux and start over.
Just not in your under pants 
Oh I'm just too tired, I need to go to bed and get some sleep. Lol
What do you mean with that?
Because even the apt doesn't work properly. There is no command add-apt-repository.
I'm from Germany, Your from France, just not your under pance. Corny joke on my part, again I'm tired and silly as usual lol.
Yup, near Paris.
You've already finished your lunch??
I have not even finish a starter with a glass of Bordeaux (with my laptop).
Something tells me that there is a vast difference between German and French when it comes to a duration of lunch time
Bordeaux, oh how fancy are we? I had no idea you were so refined. Hehe
I am so busy with my laptop so I was a bit faster today. 
I already think this may be one of the longest discussions.
I think it would take less time than trying to fix this Python version problem. I've done that a while ago and I can tell you that it is not simple.
Especially you do not have much to lose at this stage.
Just to give you some hint for future:
If you ever think of doing some tricky operation, I strongly recommend you to create a back up image of your disk using either clonezilla.org or rescuezilla.com
I am comfortable with CUI and I use Clonezilla, but my husband uses Rescuezilla (he is a GUI guy).
Then I would have to set up some things from the beginning. Is it possible to install python3.9 without overriding the python3 command to run python3.9? Because I would like to use the version anyways.
Yeah, I had to do a total reinstall of the OS after that. There is nothing like a total system meltdown to teach you what not to do next time. I felt like garbage, but it has to be done. Total wipe, reinstall, start over.
Do you think I can install python3.9 without overriding anything? Just as an addition and not as an update? I mean so I can type python3 and it will run python3.6 and I can type python3.9 to run python3.9.
That I am not so sure.
But if you make the disk image backup, you can test it out without losing anything.
Before I came back to Linux (Zorin), I had been using Hackintosh for about 3 years. Each update was a landmine 
but I survived it thanks to the Clonezilla backup 
Okay.
I would be interested to know the outcome.
Please report us the result.
How does this with rescuezilla work? So I boot it and I would get an instruction? It should somehow use a network shared folder.