What can this yellowing from the center be? Plant , in some way, splitted her stem in 2 by herself.... hope its not mutant

It is beginning of flowering and the plant wants to stretch and demmands more nutrients. So you should measure your ec and maybe increase a bit. An EC of about 1.2-1.4 should be good now.........if you are below that, increase and observe

Ich würde ihr einfach mehr Dünger bzw. einen höheren EC verabreichen. Für mich schaut sie hungrig aus Happy growing 🌸 💜

Looks healthy. At week 2-3 flower your plants are right on track bud sites are forming well, foliage is green, and structure looks solid. Keep doing what you’re doing. Just monitor humidity (keep it 40-50% in flower), temps stable, and steady watering. No signs of deficiency or stress, so you’re good to go.

chlorosis inside-out and at the top could be low S. looks like ~4 sets of fan leaves originating from a small length of stem at top indicates a very tight set of nodes due to too much light, but that's an unusual pattern of progression, if the chlorosis seen is related.. typically you'd see interveinal damage first.. so i'd lean low S. add a little epsom salt to your fertilizer mix... as long as existing levels of Mg are not too high, it's a good option that won't impact levels of anything else provided..