Flexible-Dose Trial in Early Parkinson's Disease (PD)

* Male and female participants aged 40 to 80 years, inclusive, at the time of signing the informed consent form (ICF). * Sexually active men or women of childbearing potential must agree to use acceptable (at minimum) or highly effective birth control, or remain abstinent during the trial and for 4 weeks after the last dose of trial treatment. * Participants who are capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICF and in the protocol. * Participants with a diagnosis of PD that is consistent with the UK Parkinson's Disease Society Brain Bank diagnostic criteria. * Participants with modified Hoehn and Yahr stage 1, 1.5, or 2. * Participants with disease duration (from time of diagnosis) of less than (\<) 3 years and disease progression in the 3 years before signing the ICF. * Participants with an MDS-UPDRS Part II score \>=2 and Part III score \>=10 at the Screening Visit and at the Baseline Visit. * Participants with early PD who, in the opinion of the investigator, require pharmacologic intervention for disease management. * Participants who are treatment naive or have a history of prior incidental treatment with dopaminergic agents (including L-Dopa and dopamine receptor agonist medications) for \<3 months in total but not within 2 months of the Baseline Visit. Prior and concurrent use of MAO-B inhibitors is permitted if use was initiated \>90 days before the Baseline Visit and the dosage will remain stable for the duration of the trial (ie, no change in the MAO-B inhibitor dose is permitted during the trial). * Participants who are willing and able to refrain from any PD medications that are not permitted by the protocol (including dopaminergic agents) throughout participation in the trial.

* Participants with a history or clinical features consistent with essential tremor, atypical or secondary parkinsonian syndrome (including, but not limited to, progressive supra nuclear palsy, multiple system atrophy, cortico-basal degeneration, or drug-induced or post stroke parkinsonism). * Participants with a history of nonresponse or insufficient response to L-Dopa at therapeutic dosages. * Participants with a history or current diagnosis of a clinically significant impulse control disorder (Disruptive, Impulse Control, and Conduct Disorder per DSM-5). * Participants with the presence of or history of brain tumor, hospitalization for severe head trauma, epilepsy (as defined by the International League Against Epilepsy), or seizures. * Participants with a history of psychosis or hallucinations within the previous 12 months. * Participants who answer "yes" on the C-SSRS Suicidal Ideation Item 4 or Item 5 (Active Suicidal Ideation with Some Intent to Act, Without Specific Plan, or Active Suicidal Ideation with Specific Plan and Intent) and whose most recent episode meeting the criteria for C-SSRS Item 4 or Item 5 occurred within the last 6 months, OR Participants who answer "yes" on any of the 5 C-SSRS Suicidal Behavior Items (actual attempt, interrupted attempt, aborted attempt, preparatory acts, or behavior) and whose most recent episode meeting the criteria for any of these 5 C-SSRS Suicidal Behavior Items occurred within the last 2 years, OR Participants who, in the opinion of the investigator, present a serious risk of suicide. * Participants with substance abuse or dependence disorder, including alcohol, benzodiazepines, and opioids, but excluding nicotine, within the past 6 months (180 days). * Participants with dementia or cognitive impairment that, in the judgement of the investigator, would exclude the participant from understanding the ICF or participating in the trial. * Participants with any condition that could possibly affect drug absorption, including bowel resections, bariatric weight loss surgery, or gastrectomy (this does not include gastric banding). * Participants who have a positive result for human immunodeficiency virus (HIV) antibodies, hepatitis B surface antigen (HbsAg), or hepatitis C virus (HCV) antibodies at screening. * Participants with a history of myocardial infarction with residual atrial, nodal, or ventricular arrhythmias that are not controlled with medical and/or surgical intervention; second- or third-degree atrioventricular block; sick sinus syndrome; severe or unstable angina; or congestive heart failure within the last 12 months. A recent (less than or equal to \[\<=\] 12 months) history of myocardial infarction with secondary arrhythmias is exclusionary regardless of the therapeutic control. * Participants with a history of neuroleptic malignant syndrome. * Participants who are currently receiving moderate or strong CYP3A4 inducers or CYP3A4 inhibitors (except for topical administration). * Participants with a positive urine drug screen for illicit drugs are excluded and may not be retested or rescreened. Participants with a positive urine drug screen resulting from use of marijuana (any Tetrahydrocannabinol \[THC\]-containing product), prescription, or over-the-counter medications or products that, in the investigator's documented opinion, do not signal a clinical condition that would impact the safety of the participant or interpretation of the trial results may continue evaluation for the trial following consultation and approval by the medical monitor. * Participants with a Montreal Cognitive Assessment (MoCA) score \<26. * Participants with clinically significant orthostatic hypotension (eg, syncope). * Participants with a 12-lead ECG demonstrating a QTcF interval \>450 msec. * Participants with moderate or severe renal impairment (creatinine clearance as estimated by Cockcroft-Gault formula \<30 mL/min or on dialysis). * Participants with any of the following abnormalities in clinical laboratory tests at the Screening Visit, as assessed by the central laboratory and confirmed by a single repeat measurement, if deemed necessary: * Aspartate Aminotransferase (AST) or Alanine Aminotransferase (ALT) \>=3 × Upper Limit Normal (ULN). * Total bilirubin \>=1.5 × ULN. Participants with a history of Gilbert's syndrome may be eligible provided they have a value \