A Study to Learn More About How Safe the Study Treatment Finerenone is in Long-term Use When Taken With an ACE Inhibitor or Angiotensin Receptor Blocker Over 18 Months of Use in Children and Young Adults From 1 to 18 Years of Age With Chronic Kidney Disease and Proteinuria

Inclusion Criteria: * Participants must be ≥1 year to 18 years of age, at the time of signing the informed consent/assent. * Prior participation in the finerenone Phase 3 study FIONA (19920) and not permanently discontinued from treatment by the end of treatment (EoT) visit in FIONA. * Participants must have a clinical diagnosis of chronic kidney disease (CKD) at Visit 1 which is defined as * CKD stages 1-3 (estimated glomerular filtration rate \[eGFR\] ≥30 mL/min/1.73m\^2) for children ≥1 year to \<19 years of age at FIONA EoT and at Visit 1 * Treated with an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) at optimized doses defined as maximally tolerable doses within the recommended dose range according to guidelines on blood pressure (BP) management, unchanged for at least 30 days prior to Visit 1. * K+ ≤5.0 mmol/L for children ≥2 years of age at both FIONA EoT and Visit 1, and ≤5.3 mmol/L for children \<2 years of age at both FIONA EoT and Visit 1 * Participants who have reached legal age of consent: Capable of giving signed informed consent. * Participant is able to receive enteral feeding (solid food, bottle or cup fed, feeding through nasogastric or gastric feeding tubes) with or without breastfeeding. Exclusion Criteria: * Planned urological surgery expected to influence renal function * Patients who are candidates for renal transplantation, i.e., a kidney transplantation scheduled within the study time frame * Systemic hypertension Stage 2 defined according to institutional guidelines on BP management at Visit 1. * Systemic hypotension defined as symptomatic hypotension or a mean systolic BP below the 5th percentile for age, sex and height but no lower than 80 mmHg for participants \<18 years and symptomatic hypotension or a mean systolic blood pressure (SBP) \<90 mmHg in participants ≥18 years at Visit 1. * Known hypersensitivity to the study treatment (active substance or excipients) * Severe hepatic insufficiency defined by e.g. Child-Pugh C or analogous scores. * Participants using rituximab, cyclophosphamide, abatacept, or intravenous glucocorticoids * Concomitant therapy with a mineralocorticoid receptor antagonist (MRA)(eplerenone, spironolactone, esaxerenone, canrenone), any renin inhibitor (aliskiren, enalkiren, remikiren), any sodium-glucose co-transporter-2 (SGLT2) inhibitor (SGLT2i), sacubitril/valsartan combination (ARNI), or potassium-sparing diuretic (amiloride, triamterene) * Concomitant therapy with both ACEI and ARBs together * Concomitant therapy with strong cytochrome P450 isoenzyme 3A4 (CYP3A4) inhibitors, moderate or strong CYP3A4 inducers * Previous assignment to treatment during this study * Simultaneous participation in another interventional clinical study (e.g., Phase 1 to 4 clinical studies). * Any suspected (serious) adverse event related to study intervention which led to permanent discontinuation during the FIONA study. * Pregnant or breastfeeding or intention to become pregnant during the study