staticore

I managed to solve it finally.
Unfortunately I had to remake my header/footer and not sure this is a reliable solution but it works for now and I can add my own code files and .json in the child-theme, that′s good enough for me.

If anyone else is looking for a way to fix the header/footer problem in child-theme:
All changes to header & footer are made in the parent template part files with the same name = folder Parts: Header.html & Footer.html. No name changes, no custom template parts. (I could not copy/paste settings from custom templates parts, that caused new issues.)

My files in the child-theme:
style.css
theme.json

Folders:
block-template-parts (does not include: header.html, footer.html) all other custom parts seems to work.
block-templates (includes custom files and needed: index.html)

index.html = needed to get the editor to work

I did not add functions.php

Thank again frgtech for the suggestion, it didn′t work but got me to give it another try and finally solve this.

Thank you for the advice. Any advice to try is welcome.

Unfortunately it did not work. Still no header (the code text you posted shows up instead) and can′t access the editor. Gets an error message: The editor is unable to find a block template for the homepage. (SyntaxError: Unexpected token / in JSON at position 0)

I tried another similar solution earlier but no luck there either.

May I ask how you did this?
What files/Folders do you have in your child-theme?
And have you made changes in the template-parts (not only templates) for the header/footer?

I still haven′t found any solution for it.
Tried again to activate the child theme and tried out different solutions I found when searching the topic but still the same problem no matter what.
I hope there will be some issue fix for it soon.

In the 20-22 Theme, block editor the only two sub-menus I got by default are Themes and Editor(beta).
I have customize too but got that from a plugin (can′t remember which one thought)

Unfortunately, no. I changed back to the parent theme, since I can′t have the site looking like that. Right now I don′t know what more to try than what I wrote in the list above.