Hi,
I think I did all you're mention below.
See all the steps I've just retried, please need your support :
Step 1 : upload all files and folders :
you see, also the template folder is OK :
Next Step, language :
Next, check config : (just 1 thing bad ?)
Next database config (Mysqli database, ok ?)
And last step, install data samples : (looks different than your tutorial)