It's not clear whether this is an issue with rust-bootstrap, cmake-bootstrap, or both. But the former enables +universal by default, whilst the latter no longer supports universal builds as of 2023-06:
[a4fda7b98703ff055b9dacb7e1dca58d5376d490/macports-ports]
Perhaps that's fine though...?
This did not disable the universal variant. It added universal_variant no which merely tells MacPorts base not to add the default universal variant. But the port still includes the muniversal portgroup which adds its own universal variant. To disable the universal variant would require removing the muniversal portgroup.
