@Peter_H In OP’s example, setting the URI2 to “Never” will still cause autofill to be done on that URI, because it will still match URI1, which is set to “Starts with”. Setting the match detection to “Never” just causes the URI to be ignored (as if it was never there to begin with), it doesn’t override matches that were made for other URI entries.
The current logic of matching multiple URIs is that they are combined using boolean OR, so that if there is a match on any of the stored URIs, autofilling can occur. With NOT operator in the mix, the logic would have to be adjusted slightly, as follows:
(URI1 OR URI2 OR URI3) AND NOT (URI4 OR URI5 OR URI6)
where URI4-URI6 have the NOT option enabled, and URI1-URI3 do have the NOT option disabled.
This suggests a possible implementation of the requested feature: just translate the presence of NOT URIs into a regex behind the scenes, and piggyback on the existing matching logic for the current regex detection method.