If you are doing this on a work/school account, you might be missing some permissions to create/modify flows. Especially if this is a flow that is created by someone else and shared with you - you might only have permissions to run it, but not modify it.
Also, you might not have the permissions to use certain connections, if you're using any of the Premium connectors.
Please contact your Power Platform admin (or the owner of the flow, if it's been shared with you) if you absolutely need those permissions.
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