A Study to Explore the Tissue Level Effects of Remibrutinib in Adults With Moderate to Severe HS

Key Inclusion Criteria:

* Male and female participants ≥ 18 years to 65 years of age at the time of signing of the informed consent forms (ICF).
* Diagnosis of HS based on clinical history and physical examination for at least 6 months prior to Day 1.
* Participants with moderate to severe HS at Day 1 defined as:
* A total of at least 5 abscesses and inflammatory nodules (AN), i.e. abscesses and/or inflammatory nodules
* Inflammatory lesions should affect at least 2 distinct anatomic areas (e.g., left and right axillae).
* At least 1 chronic lesion, which is defined by the presence of a draining tunnel and further meeting biopsy criteria as defined in the laboratory manual.

Key Exclusion Criteria:

* Presence of more than 20 fistulae/tunnels (both draining and non-draining) in total at baseline.
* Use of other investigational drugs within 5 half-lives, or within 30 days (for small molecules) prior to randomization, or until the pharmacodynamic effect has returned to baseline (for biologics), whichever is longer.
* Previous exposure to remibrutinib or other BTK inhibitors.
* Previous exposure to investigational Janus Kinase (JAK) inhibitors.
* Known or suspected infectious disease that is active, chronic or recurrent which precludes the participant from participating in the clinical trial as per Investigator´s assessment. These infectious diseases include and are not limited to opportunistic infections (e.g., tuberculosis, atypical mycobacterioses, listeriosis or aspergillosis) and/or known or suspected Human Immunodeficiency Virus (HIV) infection. Should it be required by local regulations and/or considered appropriate by the investigator, an HIV test can be performed to confirm eligibility.
* Significant bleeding risk or coagulation disorders.
* History or current hepatic disease (moderate to severe Hepatic Impairment (HI) as per Child-Pugh classification), including but not limited to, acute or chronic hepatitis (with the exception of Hepatitis B or C - see respective exclusion criterion above), cirrhosis or hepatic failure or Aspartate Aminotransferase (AST)/ Alanine Aminotransferase (ALT) levels of more than 1.5 x upper limit of normal (ULN) or International Normalized Ratio (INR) of more than 1.5 at Screening.
* Women of childbearing potential, defined as all women physiologically capable of becoming pregnant from menarche until becoming post-menopausal, unless they have had surgical bilateral oophorectomy (with or without hysterectomy), total hysterectomy or bilateral salpingectomy at least six weeks before taking study treatment. In the case of oophorectomy alone, the reproductive status of the woman needs to have been confirmed by follow-up hormone level assessment. Women are considered post-menopausal if they have had 12 months of natural (spontaneous) amenorrhea with an appropriate clinical profile (e.g., hormonal profile confirming menopause and/or age-appropriate history of vasomotor symptoms). WOCBP are excluded unless they are using highly effective methods of contraception (failure rate \< 1% per year) while taking study treatment and for 7 days after stopping study treatment. Highly effective contraception methods.

Other protocol-defined inclusion/exclusion criteria may apply.