Projeqtor Windows to Linux Migration

Hello,
Today I tried for the first time to migrate the projeqtor files (virtual test environment) from windows to linux for a change of server and it seems to have gone rather well. However, when I access the login page, it is impossible to log in with "admin" and the following error message appears "No log tracing possible". I don't know how to proceed to resolve this error since no log file was modified during the migration in my opinion.
Any idea on how to proceed?

The following line in ../files/config/parameters.php is :
$logFile='../files/logs/projeqtor_${date}.log';
(By default I think)

The access rights (for the log file?) :
../files/logs# ls -la
total 484
drwxr-xr-x 2 root root 4096 5 févr. 14:38 .
drwxr-xr-x 10 root root 4096 2 févr. 11:02 ..
-rw-r--r-- 1 root root 1256 2 févr. 11:02 index.php
-rw-r--r-- 1 root root 479107 2 févr. 11:51 projeqtor_20240202.log
-rw-r--r-- 1 root root 489 5 févr. 12:11 projeqtor_20240205.log

(Also don't know how to integrate lines code)

The chown worked, the strange part is i've done previously and it was pretty similar (chown -R www-data:www-data /var/www/projeqtor/)

Good point is that I'm progressing. A new error has appeared :
mbstring module not enabled (mb_check_encoding not existing) : install module and unable module in php.ini

Do you know where to get this "module" ?