Difficulty sticking to even pleasurable activities sounds like it could be depressive anhedonia. Like you, I'm suspecting I have ADHD lately (and even came here thinking of making a similar post) but this is one area where you and I differ. In my case, I find that this is one area where my previously diagnosed depression didn't make sense-- I can't concentrate/organize to save my life (almost literally), but if it's something that interests me, I lose all track of time and end up "hyperfocusing" on it. There are a number of quizzes and such about ADHD out there. A lot of them seem to focus on hyperactivity as a defining feature for some reason but the one on this site also appears to take the inattentive subtype seriously, if that makes a difference to you.

Have you been evaluated for depression? Maybe you already know it's very commonly comorbid with anxiety? (It also can often be comorbid with ADHD though, confusing as that sounds. )