I don’t think that will work because gnu-libiconv isn’t installed by default so the file will be missing from the base alpine:3.13 image. You could use a build stage in the Dockerfile to do something similar though.

FROM alpine:3.13 AS iconv-build
RUN apk add --no-cache gnu-libiconv

FROM alpine:latest 
COPY –from=iconv-build /usr/lib/preloadable_libiconv.so /usr/lib/preloadable_libiconv.so
...