の adjectives are basically nouns that get used in ways that we usually translate them as adjectives in English and other languages.
It's not actually a grammatical category of adjective in native Japanese linguistics.
"Noun which may take the genitive case particle 'no'" is certainly a better description of what the part of speech actually is.
I don't know when they changed the labeling, not sure what UI change you're referring to. (I know classic Jisho came up recently, but that change was 6 years ago, so I assume you're not talking about that).
The きれい entry has always been "adj-na" (形容動詞)..
I updated a lot of the labels for parts of speech three months ago to match updates to JMdict, the source data file. That's when "No-adjective" changed to "Noun which may take the genitive case particle 'no'".
What happened to no-adjectives?
I was explaining to a friend how no-adjectives work and I went to show them how jisho shows which adjectives are no-adjectives when I saw きれい no longer has the little "no-adjective" written right above the meaning.
And i searched up other no-adjectives I knew of and only one of the meanings had "Noun which may take the genitive case particle 'no'" written above it. This is weird because I didn't even see that written for きれい and that basically means きれい is no longer recognized as a no-adjective in jisho.
Even if they changed the UI, why would they change this part of the dictionary?