Which "#awk(1)" other than GNU one does not die & continues to awk when a variable is assigned a string with embedded newline?
FreeBSD one, via "onetrueawk" from GitHub currently, dies.
#bugIsFeature #workingAsDesigned
# Option is supported at least by "awk(1)" of FreeBSD v14 (v20240422) & GNU (v5.3.1).
awk --version
input="9
7"
echo | awk -v arg="$input" '{ print arg }'