After watching these Miraculous Secrets we can tell a couple of things. 

1: They are right before the finale. This means that their thoughts are happening right before what we see in the finale. So even though to us, Kagami and Adrien are probably together, in the Miraculous Secrets, they are not yet (and it is not confirmed that Kagami and Adrien are together, it is just assumed). 

2: Adrien is having thoughts of changing targets. Adrien clearly stated “Maybe it’s time to change targets.” This implies that Adrien is going to try changing targets and start going out with Kagami. And as we have seen in the finale, this is most likely true.

I should mention that Marinette did not directly say anything along the lines of “Maybe I should try dating Luka”. The closest thing she said was “Maybe he’ll sing me his song?” She states that she still thinks of Adrien and confused as to what to think. So this does not give us any indication as to whether Marinette has started dating Luka or not.

 

I think it is unlikely we will hear any more information about whether any characters have started dating before Season 4 airs. If we do hear any information, it will likely either be from one of the writers on Twitter/Instagram or we will get some hint on the official Miraculous Ladybug Instagram Accounts. If we do hear any new info, you will be informed on this site so stay tuned!