Hello Carlo,
The MCUXpresso IDE version 11.5 is no longer available for download; I would strongly recommend you update to a newer version of the MCUXpresso IDE.
The SDK version 2.6.0 and 26.06.00 are very different SDK versions, The one you are downloading is the 26.06.00, used in recent IDE versions; therefore, as the device are covered in latest versions of MCUXpresso IDE [v25.06], I would recommend for your assignment to use the latest version possible, as the new releases versions implements maintenance, general fixes, newer software, features and upgrades that could prevent future issues.
About the version constraints in the dashboard, when you build the SDK and select the toolchain, the MCUXpresso IDE version to use is mentioned in the description.
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Best Regards.