Furthermore, are you using both “collections columns” as well as “collections template”?
If you have the “collections columns” enabled and one or more fields specified, then those will be used as-is, regardless of what you have in the template.
Finally, your template does not initialise the tags variable. Since you are not modifying the tags variable like chaley was to remove tags surrounded in square brackets, you can simply replace “tags” with a column lookup on your source collections. So if your custom column lookup name is #koboshelves then I think your template would look, in full, like:
Code:
program:
# Remove tags listed in tags_to_ignore
tags_to_ignore = 'danach, kurz';
list_join(':@:', list_difference($#koboshelves, tags_to_ignore, ','), ',')
This seems to work when testing in my own library using the Template Tester.