Unable to debug: variables not accessible or with wrong values

[Mark81]

Qt 6.2.0, QtCreator 5.0.2, Ubuntu 20.04 Desktop (both dev and target machines).

From my dev machine I'm trying to debug applications on the target.
I'm unable to do anything because most of variables are set as "not accessible" and even when they are "accessible" their value is wrong, example:

As you can see:

1. file is not accessible even it's a local variable
2. filename seems to be an empty string, while it has a proper value (the file was actually opened)
3. line seems to be an empty string, while it has a proper value as printed out by qDebug() call

It's a pain to debug in such a way... would you please help me to understand why it does not work?
What I have to check?

Here the settings of GDB:

I see the warnings about "solib-search-path" and "sysroot" but as you can see in the pictures above I tried to define them.