if there are no upheavals within the UN, numerous sanctions and military embargoes against the DPRK remain active, to which Russia has also officially joined.
This does not mean that Moscow cannot "collaborate" with North Korea to help it strengthen its defense system, but it will do so possibly by trying to disguise supplies/aid with systems that the DPRK already has at its disposal, or with systems also several to which it could potentially acquire also outside Russia.
Therefore
1) In the short term, a significant increase in the number of MiG-29s is possible
either with direct supply of second-hand aircraft from Russian stocks or even in newly produced kits which can then be assembled locally (all old and new with modernization)
2) I don't think that Moscow supplying SU-35 would be too obvious to the whole world, but it doesn't take away from the fact that they could supply deeply modernized SU-27 type SU-27SM/SM2
3) In the medium term, help to create a jet trainer aircraft with CAS capability
4) In the long term, barring global and UN developments, not the delivery of a possible LTS (Legkiy Takticheskiy Samolyot - Light Tactical Aircraft), but collaborating for the creation of an indigenous North Korean project for a combat aircraft that could benefit from what was created for LTS, but with a slightly different design to be able to state that it is not an LTS.
This new fighter may be built/assembled officially in DPRK with parts made locally and others that could be supplied by Russia away from prying eyes.
