We are also facing the same issue, we are running on Splunk Cloud 8.2.2202.1 and Alert Manager 3.0.11.
Everything is throwing JS errors in all the settings pages like incident settings, user settings, external workflow actions, etc.
Please address this issue. Also, when we try to comment and close the alert after assigning, we cant do so. Instead, the alert becomes unassigned. Need solution for this as immediately. Please solve this because it can impact the business continuity to some extent.