I guess you installed V8.0.3 on new forlder instead of erasing existing code.
You lost the tool/parametersLocation.php file.

Yes we have installed V8.0.3 on new folder.
But the tool/parametersLocation.php file is the same in both folder (8.0.3/7.4.4).
it contains :
<?php
$parametersLocation = '../files/config/parameters.php';

But the tool/parametersLocation.php file is the same in both folder (8.0.3/7.4.4).

Yes, but this file was not present on new folder, so you had configuration screen displayed.
Then it recreated the ../files/config/parameters.php, possibly with different values, and as DB was already populated, the parameters were not moved back to DB, so I guess parameters.php file on both folder is different, or at least some global parameters have been erased in DB...

Ok why not.
I have a backup of DB before update 8.0.3.
If global parameters were stored in DB, where are they in DB ?
Thank you

in table parameter.
They are parameters where idUser is null

Ok thanks.
I think I understand.
If a global parameters is set in 'parameters.php' AND in DB,
then it is read first in 'parameters.php'.
So if I remove a parameter in .php (example $paramMailSmtpServer), the value in DB will be read and I should find my previous value (before update) ?

That's it

Perfect. Thank for help