The Copy functionality in the Power Platform Admin Centre can be very useful for creating things like testing and training environments based on the environment you’re currently using in Production, and be an everything copy with data and customisations, or just customisations.

Microsoft provide a decent amount of information about this on this page, including about situations where the environment you want to copy over can’t be found. This list doesn’t seem to be exhaustive though – after experimentation I determined that environments which are not operating in Managed Environment mode cannot be overwritten by a source environment which is in Managed mode. The environment will just not show in the list of target environments.

So – to fix this – all you need to do is to change the target environment to be a Managed Environment, by following the steps in the Power Platform Admin Centre. From my reading online and personal experience- it is not a very risky move in general – you can disable this mode quite easily. The riskiest part of a move seems to be making sure that the auto claim policy (for the licenses) is set up correctly.

Once Managed Environments are enabled, the environment should now show in the list of target environments – as long as it fits the other criteria 🚀