A Clinical Trial to Evaluate NB-4746 in Participants With Amyotrophic Lateral Sclerosis.

The purpose of this trial is to learn about the effects of NB-4746 compared with placebo in people with amyotrophic lateral sclerosis. The questions this trial aims to answer in comparing NB-4746 to placebo are: * What adverse events associated with taking NB-4746 are reported during this trial? (An adverse event is any sign or symptom that participants have during a trial. Adverse events may or may not be caused by treatments in the trial.) * How does NB-4746 move into, through, and out of the body of the participants? * What is the change in the level of neurofilament light (NfL) in the participants' blood? (NfL is a marker used to measure the extent of damage to the nerve cells.) This trial has 2 parts. The trial doctors will start Part A before starting Part B of the trial. Participants have an option to enter the open label extension after completing Part A or Part B. Part A: Participants will be randomly placed into 1 of the 3 groups. There are equal chances to be assigned to either group. Group 1: Participants will receive NB-4746 capsules at a low dose to take by mouth twice daily for 1 month. Group 2: Participants will receive NB-4746 capsules at a high dose to take by mouth twice daily for 1 month. Group 3: Participants will receive placebo capsules to take twice daily for approximately 1 month. Part B: Participants will be randomly placed into 1 of the 2 groups. There are equal chances to be assigned to either group. Group 1: Participants will receive NB-4746 capsules at a dose determined by Part A to take by mouth twice daily for 12 weeks. Group 2: Participants will receive placebo capsules to take twice daily for approximately 12 weeks. None of the participants, trial doctors, or trial staff will know which treatment the participants will receive during Part A or B. Some trials are done this way because knowing what treatment the participants receive can affect the results of the trial. Doing a trial this way helps to make sure that the results ar