If you live in the US, and have medically-diagnosed ADHD, you can write your HR to let them know you have a disability under the ADA and that you would like accommodations. You must have it in writing (ie email), otherwise there’s no proof. Once you do this, you become protected in the vent your ADHD is negatively affecting your work.
Of course YMMV, and employers might still try to oust you if they think you’re not capable. But having a paper trail will certainly help.