I read the emboldened sentence, but I still don't get what Non-addressed Decisions' past function is?
What's their function now?
Aren't Directives "an instrument that was directly applicable but lacked direct effect"?
Directives now have Vertical Direct Effect. The No Horizontal Direct Effects rule has exceptions like the Wide Definition of States, Incidental Horizontal, Indirect Effects through National and Primary EU Law, Indirect Effects through Medium of European Law.
Note I'm asking about JUST type 2. Robert Schütze. European Union Law 2 ed. 2018. pp 92-93.
This development is now recognised in Article 288(4) TFEU that allows for two types of decisions:  decisions specifically applicable to those to whom it is addressed, and  decisions that are generally applicable because they are not addressed to anybody specifically.
bb. Non-addressed Decisions
While not expressly envisaged by the original Treaties, non-addressed decisions (decisions sui generis) had become a widespread constitutional phenomenon within the European Union.89 The Lisbon Treaty has now ‘officialised’ them in Article 288 TFEU. But what is the function of these decisions? In the past,
the Union had recourse to these decisions – instead of regulations – to have an instrument that was directly applicable but lacked direct effect.