Step 1: Install dwebp (part of webp package)
apt install webp
Step 2: Convert Files
dwebp image.webp -o image.jpg
Converting in bulk:
for file in $(ls *.webp); do dwebp $file -o $file.jpg; done
This will convert all files in the current folder (with the .webp extension) to JPG and append .jpg to the file name.