The "purpose" of the MRBM may have been to flaunt Russia's supposed nuclear capability post-withdrawal from the MIRV limitations of the SALT/START treaties and thus give poor senile old Biden another wet-pants event. The USA, as you know, complied with the treaties and reduced the ratio of missiles to warheads so as to reduce the first-strike advantages MIRVs were thought to create. Putin may be hoping that by demonstrating the Russians have at least one sort-of-reliable delivery vehicle that can throw 36 small warheads at a city, the tiny trickle of aid the USA has given to Ukraine (always with absurd restrictions further reducing its paltry worth) will not be increased during the brief period before the orange vermin waddles back into the White House and proceeds to hand Ukraine to Russia on a tawdry gold-painted platter. Given Russia's enduring success in terrifying our "leaders" into near-total inaction, this strategy may not be entirely foolish.