I'm experiencing the same thing. I also flirted with Lucanis maybe once or twice very early in the game before deciding on another character, and haven't done any other flirting recently. I don't want to re-start my entire game for this bug, and while I can choose the flirt option and then immediately choose to cut off further romance in the next dialogue option, I'd rather not be locked into having to flirt with him in this scene at all when it's not what my character would do at this point of the story. Very odd bug, and I'm pretty sure it's unintentional. At least I hope it is!
I tried a variety of different dialogue options in the scene before the forced flirting and they all led to the same point, where I can only flirt with no other choice. So I don't think there's a workaround.
ETA: I'm experiencing this bug on a PC (Steam/Windows), rather than a PS5, so it's happening on multiple platforms.