I've come to think this really depends on the person. I realized that I naturally intermittent fast, because it seems to work the best for me. Normally I eat my last meal of the day ~ 8pm, and nothing but coffee, tea, or water until 11am or 12pm the next day. The only time I eat something in the mornings is if I'm doing a workout or something active early in the day. Occasionally I'll feel hungry and eat something, but otherwise, I normally feel sluggish and slow if I eat breakfast. For my other meals, I actually eat a ton of food, around 2,500 calories on average.

On the flip side, I know multiple people who have tried the same and have your exact experience. Oddly enough, three of them had tried keto and had great results where I personally didn't. I know there's no real correlation there, just thought it was interesting. Try keto maybe?

If you start to restrict carbohydrate intake this helps with the low energy and irritability in my opinion. Been doing a 18-6 fasting since May (with some cheat days) and feel incredible.

Do you have to get up quite early in the morning? Only reason I ask is because half the day being the time until 12 is surprising -- after your midday meal, if you've constructed your meal properly, you should ideally not be hungry until dinner. I think IF needs to be paired with a mindfulness about what you're eating -- having toast with butter for lunch will not work.

Usually like 7:30. Had to get kids to school. I always eat pretty wholesome food with lots of whole grain and vegetable. When I was doing IF, I needed a big lunch to regain my senses and frequently didn't make it to 6PM without needing another dose of food. I suspect I was fitting my normal calorie intake in that window. If the goal was to somehow trick my metabolism into wanting fewer calories, I don't think it worked at all.