In order to use immutability, you have to use GFS retention. Do you have GFS selected on the retention page? If you want, you can post an image of your retention page here on the form.
You cannot change immutability settings on an existing bucket. You need to create a new bucket on that account and enable immutability at creation time.
We know this. We created account and enabled inmutability at creation time.
If you see our screenshots, all parameters are well configured both in wasabi and msp360.
But in msp360 agent, option for inmutability is greyed, and we don't know why. Inmutability is not working because we created a test backup with GFS enabled and we have deleted this backup.
I think inmutability in msp360 + wasabi storage still does not work.
It's enabled as far as I am aware - you are referring to an old post. Your screenshots were confusing as one seemed to show the bucket as not having Immutability selected (from agent) and the other was at creation time, but not after creation. So I am not sure if something happened at creation time or the agent is not picking up the setting for some reason.
Where are you trying to create the backup plan? From the agent or from the management console? If you have not tried the management console, please try that.
If all else fails, then I think the best option is for you to open a support case.