Nit - the goal of economic activity in the USSR was not entirely the accumulation of capital - it was production of what were considered necessary goods. Televisions, automobiles, bombs, tanks, that sort of thing.
This is, in some ways different from economic activity for the purpose of making more money (Which, in addition to producing things like television, automobiles, bombs, and tanks, also ends up producing things like advertising.)
That's a good point, but according to my knowledge this was a matter of degree rather than quality - almost all countries have or have had such production in whole or in part, implemented through subsidies and especially during wartime or other hardships. It's also to be expected when production is at least nominally democratic and central, it's not all about simple appearances. But what distinguishes a socialist society from any other is that goods would no longer be produced as commodities - i.e they are not imbued with the form of labour which tailors for exchange over use. Capital tends to totalize all labour into that which works for exchange over use, e.g. it has subsumed artwork and non-tangible goods from things of use into things with exchange value and a use-value. But exchange value tends to prevail and even changes the concrete form of labour, e.g. advertising as you suggested, and also, for instance, music sold on platforms like Spotify to maximize revenue, such as shorter, highly-replayable and segmented songs. Capital exists no less for the state, which will tend to share the same motivations as other capitalists, especially since it must buy and sell to other states or private individuals abroad.
This is, in some ways different from economic activity for the purpose of making more money (Which, in addition to producing things like television, automobiles, bombs, and tanks, also ends up producing things like advertising.)