Regarding export of J-20 to Pakistan.
I don't think Pakistan will pursue this option for the time being anyway unless India nears a 5th gen platform. The fastest they can get it is F-35s, which would mean alot of changes to their existing infrastructure to keep it away from Russian hardware, imagine UAE couldn't agree to those strict conditions. Next is their own development, I don't think they'll have anything credibly operational in next 15 years and they re pursuing something in same wt class as f-31, which would be alot more mature platform than J-20. Apart from that, there is also news of PAF working with TAI platform, so tbh, PAF has more credible options than InAF regarding 5th gens.
And again, Pakistan as a policy will not introduce 5th gen unless India does so.
Frankly speaking in 15 years, a credible export oriented j-20 variant would be more than good enough to counter any Indian 5th gen option locally developed.