Search notes:

Overpass API function suffix

suffix(…) returns the value after the last digit (or so?).

The following query finds all addresses (nodes and ways) in Pfungen whose house number is not completely numerical:

{{geocodeArea: Pfungen }};

nw
  ['addr:housenumber']
  ( area             )
  ( if:  suffix(t['addr:housenumber']) > '' );

out geom;

See also