A Study to Evaluate the Safety, Tolerability, Efficacy, and Drug Levels of CC-97540 in Participants With Relapsing Forms of Multiple Sclerosis, Progressive Forms of Multiple Sclerosis or Refractory Myasthenia Gravis (MG) (Breakfree-2)

Cohorts 1 and 2: Participants that cannot complete the 9-Hole Peg Test (9-HPT) in at least 1 hand in <240 seconds unless extenuating medical conditions unrelated to MS prohibit this.

Participants that cannot perform a Timed 25-Foot Walk Test (T25FWT) in < 150 seconds.

Presence of other confounding peripheral nervous system disorders or other disorders that may impact muscle strength (eg, myositis) or cause weakness, stroke, chronic inflammatory demyelinating polyradiculoneuropathy, Lambert-Eaton myasthenic syndrome.

Other protocol-defined Inclusion/Exclusion criteria apply.