Most of Russia's trained cadres have been destroyed. Survivors are constantly being recombined with other remnants of previously operational units, but it takes time to build cohesion.
Many of the convicts and untrained conscripts have been frittered away around Bakhmut. Some training is being done in Belarus because their army still has long serving non-coms and officers, though none have served in Ukraine. In short, Russia is trying to rebuild an army as it fights a war it is losing, complicating the attempt. JL
Nick Walsh reports in CNN:
Russia is unlikely to see strategic success in any potential offensive in Ukraine this spring due to limited support on force ratios, equipment and logistics. There are severe constraints to their ability to really backfill the losses that they have suffered in Ukraine, "which is why you see them reach out to international partners to try to fill the gap." These limitations might not prevent Russia “from trying to launch an offensive,” but their “ability to change the course of the conflict at the moment is constrained.”