I think I found a rather specific bug, might be related to
I use metabase 0.25 and a SQL database.
I used to join two tables in my data model, the main table had the primary key field, the secondary table had the foreign key field.
I realised that when I use only the query builder to build queries I can´t filter anymore on the primary key field (as it exists only as a link to the secondary database).
As this hard join is not really used in our setting anyway I decided to remove the join in our data model and since then I can select the former primary key field (what is now defined as a category field) as a filter in my query builder.
BUT: when I create a dashboard for this question and want to use the same field as a dashboard filter (category filter) on dashboard level, the list I get to choose the filter field from is still from both (formerly joined) tables and the former primary key field is still not selectable as it works as a link between the two tables:
In the picture you can see the link "receiver identifier" between the two tables, I can´t select this field als filter:
It looks like the information about the de-joining of the two tables did not update everything in metabase? at least the filter lists are not up to date.
I synced the database several times already and also created a new dashboard. Same effect.