Is it common for autistic people to have a hard time focusing on things that require great attention?
As a musician, I have found that a majority of the time I'll sit down to practice and after 5-10 minutes I will be very tired and groggy, finding it almost impossible to stay awake and focus. This makes me agitated and depressed, and I can't continue.
Sound familiar?
Depends. If you are sleep deprived or burnt out, then no, you really can't focus. That requires a lot of mental energy, and if you're "running on empty", forget it.
ADHD is, as others mentioned, a common co-morbidity. However, the most interesting argument that some have against the existence of ADHD is the fact that if given something like a video game they like to play, many people with the condition can sit for hours at a time quite highly focused. They are given consequences and rewards in a video game. It is dopamine triggering. Now, it may be that this is a key element to how to focus and accomplish things if you do have ADHD. Does whatever you are tasked to do have consequences for failure and rewards for success? Two, do these consequences and rewards come at a frequency that it keeps the person engaged? Three, is whatever they are doing actually interesting to the person?
Autism, when combined with a special interest, often leads to intense focus, intrusive thoughts about the topic, etc. If a special interest becomes a career, then I would never stand in the way of an autistic person on a mission, because this person will run you over and keep on moving. For example, like him or not, Elon Musk is highly focused and doesn't give a thought to all the people who hate him or is trying to short his stock or all the bad media coverage or any of that. He pushes forward, mind on the mission, and I would never make bets against him. We can make a list of other highly influential people in the arts, sciences, business over the many years that had a lot of autistic traits, among them an intense level of focus on their special interest.
So, it may be that music might not be your special interest right now, or you're just mentally tapped out right now, or if you do have an ADHD condition you may have to create several short-term goals that you can stepwise attain, like levels in a video game, get the dopamine hit, next goal, dopamine hit, and so on.