We've all made mistakes when it comes to taking jobs that have turned out to be different in reality to what was advertised. Sometimes we take a risk in trying something new and realise it isn't for us. I'd far rather, as an employee, have people working for me who had shown willingness to step out of their comfort zone during their career, rather than people who had just stayed ploughing the same furrow for 20 odd years.
A few years ago I took on a job that on paper looked like a dream opportunity - but the reality was, it was largely administrative (as opposed to the strategic job it claimed to be). On my first day I realised I had made a mistake when it emerged I was in charge of the admin behind a shared inbox receiving over 500 emails per day - I was supposed to be leading a team and creating new products, and instead I spent all day every day just trying to keep on top of a constant barrage of admin. It caused me a huge amount of stress and I actually became quite depressed as a result. I was worried about leaving so quickly, too, but I needn't have worried - I had no problem at all finding a new job. I lasted 9 months - but I wish I'd had the courage to leave even sooner.
So, in short, moving on again so quickly won't look bad or be a barrier to you finding a new job, if that's ultimately what you decide.
However, as others have said, see if you can find a solution first.
Raise to your manager that you are spending a huge proportion of your working time on the management of this data system, which is a responsibility that was not in your job description. Make it clear that if this responsibility had been in the job description, you would never have applied for the job.
Further to this, be honest about how much of a struggle you are finding this data system due to your ADHD.
Your workplace legally needs to put in place reasonable adjustments to help you with your ADHD. They also can't ask you to take on duties outside of your JD without your consent.
If the role can be meaningfully adapted so that you are no longer doing the work you dread, then there will be no need for you to leave.
If after making adaptations, it's still not working for you, then please don't be afraid to find something else.