transition-behavior is already supported in all major browser engines. Though while it is meant to apply to all discretely animated properties, some properties, especially display but also content-visibility and possibly others are not affected by it in some engines yet.

At the same time, there is currently no CSS-only way to feature-detect that.

Therefore, I think it makes sense to add a keyword to the named-feature() function for the @supports rule for that (see the resolution in #3559 (comment)).

Sebastian