If you never did any about:config changes those would be the FF default settings. So what are you asking about?

RexaFire said

I never modified things in about:config but there many modified things?Why?

If you make changes in Options/Preferences then it will reflect in about:config as user set. Any (legacy) Extensions you installed may make changes or add Preferences in about:config as user set.

Firefox also stores a lot of internal data like update checks and version numbers in special prefs that always show as user set.

WebExtension can't add settings to about:config like was possible with Legacy extension. If you used the profile with Firefox versions that supported Legacy extensions then you may still see preferences from those extensions.

How do I now fix it? I restored all to default.

Can you clarify what preferences setting in particular bother you?

As explained above, there are a lot of lines showing on the about:config page that Firefox uses internally and should be left alone. If you would reset such prefs the Firefox will recreate them automatically.