Hi milanweiss,
do you mean this article? https://github.com/shopware/platform/blob/6.2/src/Docs/Resources/deprecated/2-internals/1-core/20-data-abstraction-layer/045-custom-field.md
Normally the new DAL section in the „References internals“ area was going to replace this but we seem to have missed this during the restructuring of the documentation.
You pointed out that even more guides are missing. Could you give us more examples so we can look into it?
In general the „old“ documentation is still there inside the repository: https://github.com/shopware/platform/blob/6.2/src/Docs/Resources/deprecated/
All How To guides should still be available in the How To section.
We are sorry for the circumstances.
Best regards
Tobias