<p>Long-term cognitive impairment is a recognized sequela of the post-COVID-19 condition (PCC). While it is unclear how acute COVID-19 severity contributes to these lasting deficits, some evidence suggests that critical illness may lead to cognitive deficits similar to post-intensive care syndrome. This study examined long-term cognitive, mental, and physical health in patients with varying acute COVID-19 severity (mild to critical), alongside patients critically ill from non-COVID-19 causes. We conducted a bicentric prospective observational study comparing patients with PCC after mild COVID-19 (<i>n</i> = 30), those requiring ICU care for acute COVID-19 (<i>n</i> = 14), and patients with prolonged non-COVID-19 ICU stays (<i>n</i> = 7), all assessed ≥ 12&#xa0;weeks post-onset. Comprehensive neuropsychological assessments were conducted alongside evaluations of physical impairments, psychiatric symptoms, fatigue and health-related quality of life. Overall cognition was comparable between the mild COVID-19 and ICU groups. However, the mild COVID-19 group experienced higher cognitive fatigue and lower memory satisfaction than both ICU groups, along with higher rates of anxiety (59% vs. 15%) and depression (38% vs. 15%), and reduced mental health-related quality of life compared to COV-ICU patients. Long-term cognitive impairment occurred in PCC patients and ICU survivors, irrespective of acute disease severity. Patients with mild COVID-19 reported greater long-term psychological distress.</p><p><i>Trial registration</i>: This study was retrospectively registered at the German Clinical Trials Register, DRKS00025523 on 21 June 2021 (<a href="https://drks.de/search/de/trial/DRKS00025523">https://drks.de/search/de/trial/DRKS00025523</a>).</p>