The weblate sidebar shows explanation, labels and tags as being editable, but tags listed in the side bar are not shown in the dialogue.
Expected behavior
See attached screenshot, "c-format" tag:
This tag was read from a .pot file and is probably considered read-only/non-editable in weblate.
So I observed the following, a little confusing behavior:
The behaviour to me looks like the tag read from the .po file is read only, which is good in principle.
But: Should we be able to remove it for false c-format tags in the .pot file or should we say "fix your .pot file?"
So for the current behaviour the only enhancement that I'd like to see is that the non editable tags are indicated on the sidebar and/or shown in an non-editable field of the dialogue.
Screenshots

That's indeed confusing. The flags are collected at several levels:
Questions (we're getting into a discussion here ;-)):
The flags were originally modelled based on GNU gettext ones and grown into [a huge list](https://docs.weblate.org/en/latest/admin/checks.html#customizing-behavior-using-flags.
As for the editing interface, please see https://github.com/WeblateOrg/weblate/issues/1567.
Flags and labels are different - flags configure Weblate behaviour (and thus it makes sense to provide component-level ones), while labels are user categorization only.
The interface will now explain this:

Wow!
Maybe add an 🛈 with a link to https://docs.weblate.org/en/latest/admin/checks.html#customizing-behavior-using-flags behind "Inherited flags"?
Like: "Inherited flags 🛈" ?
One question remaining:
If this is not possible yet, I think it would make sense, since it would allow you to find strings with a certain behaviour.
Good idea, I've added it.
Searching by a flag is currently not possible. This would be currently problematic to search for a flag as these are stored in a text field in the database. So searching for "c-format" would yield "ignore-c-format" strings as well. The search also could be expensive because of merging flags from different sources...
Thank you for your report; the issue you have reported has just been fixed.
Most helpful comment
The interface will now explain this: