Rather than the swift advances of the German's designs, that pushed the Soviets to improve theirs, the Japanese armoured vehicles and airplanes had another level of quality (due to their resources).
Said that, did the Soviets took their "outdated" equipment to face the Japanese in the East borders? Like the BT series? or the biplanes that were used in Jajin Gol?
Yes. Far East Soviet forces were naturally last in priority when it came to new AFVs. In part the local units updated their own vehicles with applique armour and bigger guns for the lighter tanks. Upgrading some tank units to T-34-85 tanks only began in the spring of 1945, and even then this happened only partially. There was also an interesting organizational proposal made at this time. Even though as of 1941 only officers could be tank commanders, an exemption could be made for senior NCOs who were very familiar with T-26 and BT tanks.
After Germany surrendered, there was a large scale transfer of complete units from the European theatre to the Far East. These units came with new tanks since no one was using T-26es and BTs in Europe by that point. By August 5th, 1945, there were 6234 functional tanks and SPGs of all types in the Far East. Of those 1272 were T-26es, 797 were BT-7s, 101 BT-5s, 304 T-38s (about 120 had upgraded armament and armour). In total there were 2787 obsolete types of tanks in action.
When it came time to assign these vehicles, the really obsolete types were dropped and the focus was on the BT-5, BT-7, and T-26. For instance, the 6th Guards Tank Army had 85 M4A2(76)W tanks, 416 T-34-85, 193 SU-100, 26 SU-76, 177 BT-5 and BT-7, and 22 T-26 tanks. Still a large number of obsolete tanks, but the proportion is more skewed towards modern types.
When it was actually time to drive into Manchuria, the modern tanks showed that they were much more reliable than old worn out ones. All 11 T-26es that actually embarked on the journey broke down in the first few days. Only one BT tank was left behind before the march, but only 57 made it to the end. None of these were combat casualties, all the losses came from the forced march in extreme heat.
Sources and further reading
http://www.tankarchives.ca/2018/04/far-east-conversions.html
http://www.tankarchives.ca/2018/09/far-east-modernizations.html
http://www.tankarchives.ca/2014/03/up-armoured-bts-in-far-east.html
http://www.tankarchives.ca/2014/04/soviet-tanks-in-far-east.html
http://www.tankarchives.ca/2018/03/upgunned-t-38-trials.html
http://www.tankarchives.ca/2018/08/upgrade.html
https://www.tankarchives.ca/2022/01/starshina-commanders.html
P. Samsonov Sherman Tanks of the Red Army.