I had a "good run" of about 6 years of exercising and eating healthy in my twenties. That's almost a decade ago now.
While I don't regret any lessons learned in life, I would like to be able to go back in time and share these lessons of kindness to myself. Maybe then my health journey would not have ended as it did back them. But as I can not, maybe someone here, who's as strict as I was back them might benefit from them.

1) Eating healthy all week is not a punishment. Thus the "cheat meal" is not a reward. Eat the healthy foods you enjoy and skip the rest. Eating healthier should feel good and easy, not like you are proving your level of self-discipline each meal.
2) If you are starting from flabby, work on building muscle first, even if the big goal is to lose weight. So don't start with a major calorie deficit. Eat normally (but healthy!) and build muscle while you learn the habit of daily exercise. Adding calorie deficit later, when you have built muscle to actually use the calories you consume can make your journey easier. Trying to lose weight and build muscle at the same time can kind of be like filling a leaking bucket. You would use way more energy for way less results.
3) If you can't do the move that the instructor is doing, do an easier version. Or even just jog in place. Just keep moving. You won't feel like such a failure, as you did if you just stop and stare at the screen in pain.
4) Hormones and bloating affect your body some days. It's not you "going backwards" or "not having any gains". Your body is a living thing and you can't micromanage it into constant, linear success.
5) People who have been on their health journeys longer (or sometimes just someone who likes to run their mouth) will give advice that absolutely won't work for you. Worst case, that advice will make you fall off your journey because it makes you hate the new routine (for example eating healthy in a different way) if the standard they're trying to make you follow is really rigid or doesn't fit your life. They're not going to live with the choices you make. And you failing because of their advice won't affect them. So do not listen to the know-it-alls like their word is law. Take what works and leave the rest.