It seems that “Some text Widget” and the “Lorem Ipsum …” is hard coded in sidebar.html.twig
But altering it in there would compromise future update or theme migrations, am I right?
So, is there another way to overwrite this part, writing only in /user/pages?
Sounds like an inherited theme would provide that for you. You can learn more about that approach at https://learn.getgrav.org/themes/customization#theme-inheritance
That works perfect. Thank you, Paul.