The comment you replied to says that they can’t meet demand due to insufficient supply (due to grounded aircraft). Very high occupancy is consistent with that. If Delta suddenly had half as many aircraft they would always be full too.
Counterintuitively, yes, because air travel is a Cournot good and you grow/make money by expanding supply (more planes), which they can’t
Which they can, because Russia produces aircraft domestically.
In theory yes, in practice deliveries of domestic aircraft have stalled. The Sukhoi Superjet 100 for instance hasn't had a delivery in 2 years and I think the Tu-204 also did not get any deliveries though they expected some this year. It is however also very hard to find out what exactly is going on, because the information regarding civil aviation is quite restricted nowadays.
Barely. The Sukhoi Superjet trickles out of the factories, and the other two projects have been delayed again and again.
They have a big problem with producing modern engines and won’t catch up with the demand without Western suppliers for at least a decade, which means that in a couple of years this is going to be a huge problem.