My ADHD-like symptoms (it's not officially diagnosed but boy howdy I'll eat my hat) are so bad that when I discovered I'm plural and learned our names (an absolutely MONUMENTAL life milestone by the way) I was completely infatuated with studying concepts of plurality for about three days until the novelty wore off and I fucking lost interest and stopped like I never heard of it just like literally everything else I ever try to do XD
Yeeeah, this sounds like ADHD alright... you get hyperfocused on something for some amount of time (some of our fixations lasted over 10 years!), but then you suddenly just lose them to the point where you can't even try anymore. Sometimes temporarily, sometimes forever, but always indefinitely.
Our only advice would be to try to get medicated if you can't ever find any ways to navigate the ADHD... it's the only thing that worked for us, but most others don't have it as bad as we do.