@RenewedRebecca LispWorks checks all points and contains a fully-fledged UI framework. You may want to check it out.
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I prefer the LispWork suggestion, but there is also Eiffel
https://www.eiffel.com/eiffelstudio/
https://www.eiffel.com/eiffelstudio/screenshots/
I never used the portable GUI library, but the language is very nice to use.
