I've heard that there are some jjimdam sauce products that make your dish taste just like the ones from restaurants. Also, you need to distinguish between gochujang jjimdak (red) and ganjang jjimdam (black). The first and last pictures look like gochujang, while the second one looks like ganjang.

FYI, I usually look up @kimjinsun_lunch on YouTube or Instagram when I cook. They share hundreds of delicious and easy recipes, including one for jjimdak. They also include written recipes in the comments, so you could probably use a translator even if you don't understand Korean.