find sed

# Trying to find all .txt files in a deep directory and replacing
# specific occurrences of spaces and tabs with a single space.
# f.ex. replacing "aa      bb" with "aa bb".

# This works:
find my_dir -iname "*.txt"

# This works:
sed -E -i '' $'s/aa[ \t]+bb/aa bb/g' file.txt

# Together, they do not work:
find my_dir -iname "*.txt" -exec sed -E -i '' $'s/aa[ \t]+bb/aa bb/g' {} +