yellowing tips . burned or not?

Yes, feeding too often or too much, maybe both.

Wait. This could mean anything (see the conjectures here) or nothing at all. As long as this doesn't spread or get bigger, sit back and don't freak out. You've already made it to flowering, so the rest will work out, too. Please don't forget to feed additional PK in a week or two ;-)

Too close to the light - but it's very minor. What's your light schedule? Is it dimmable? Think minor changes. Raise the lights half an inch or dim them if you feel you have to. But this plant is happy enough.

Ein wenig zu viel Stickstoff 😉aber noch im Rahmen..

Those are signs of a slight nutrient burn. But it's not forming claw-like leaves, looks strong and healthy. I'd say there's no reason to worry.