Royal Gorilla

I wouldn't worry about it as you're only 3 weeks or so from a lovely harvest. What I would suggest is removing some of the dead leaves and some of that lower growth not receiving much light, this will divert energy to the top of your plant. 🌱👍

You’ve been doing great. Looks like you’re getting to the end of flower! It’s going to be perfect!

Judging from the pics and your diary I would say this the normal nitrogen deficiency you see in late flower. The plant is basically finishing up... you have nothing to worry about ... Good job.