@Roderick Zoeteman - Welcome to Microsoft Q&A and thanks for reaching out to us.
Currently, it is not possible to disable or enable Maintenance Configurations created by Azure Update Manager.
As a workaround you can specify the end date time for the schedule or can put a future start date and time.
Maintenance Configurations are used to define maintenance windows for your Azure Arc-enabled servers and specify the updates that should be installed during those windows. Once a Maintenance Configuration is created, it cannot be disabled or enabled. Instead, you can create a new Maintenance Configuration with the desired settings and assign it to your servers.
Hope this helps. and please feel free to reach out if you have any further questions.
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