I do my all my weekday workouts at 6:15am and have no real problems with hard efforts unless I have a bad night of sleep and/or don’t fuel well the day before.
We wake up around 5:15am every morning, have a light snack, and then I am straight on the bike. I try to eat something on the bike and have a recovery drink during cool down, which helps a lot and I could do a second workout later in the day if I wanted to.
I’m mostly a cyclist these days but from a triathlon background up to IM distance, so 2 workouts a day is what you have to do. It took time to get used to early morning workouts, but in Texas you have to do it!