Guys, the main three colas leaves started to yello...

Definitely nutrients issue-exactly what -i cant tell.
But you pot container is way too small for that plant and my guess is that what causes plant to loose vigor amd change colors.the root cannot intake as bounded roughly in there.
If you can dry soil complete and get a friend to help transplant to bigger pot.
Then flush massively only water .
This will refresh things in there

Congratulations on the signs of reaching the end of your first grow! It all looks beautiful. And yes of coarse you'll be able to get those leaves away. Do a wet trim when its time, getting the largest fan leaves off, probably will end up being many of those yellowing leaves. I agree with the flushing of plain water, although a friend who grows for the dispensaries believes that's like starving someone. I think that is absolute nonsense. You don't want your weed tasting like nutrients right? That's partly why we flush to get those extras bits up and outta there. I didnt know it was called the senescence thanks @b4rns

It’s called the senescence ... known as the fade ... every beginning has an end ;)

Greetings. Move your lights up. 18" away from top cola should be enough. Don't raise your nutes you are at the end of the grow and you might end up having a harsh smoke with too much nutrients my brothers. Hope this is helpful to you.. good luck!!!

You are 9 weeks into flowering, you should be giving them only water.
The yellowing is completely normal, the plant is nearing the end of it's life and so is dying.

You should back off the nutrients and use plain pH'd water for awhile as i can see signs of nutrient burn and heat stress. Also, for that late in flowering your room humidity is way too high. Should be around 40-50% maybe even less.
Yes, the affected leaves can be removed at anytime. Hope this helps