As far as "spheres of influence" are concerned, they did denounce it
On Christmas Eve 1989, Soviet lawmakers had indeed admitted the existence of the secret protocol of the MRP [Molotov-Ribbentrop Pact] and condemned it with a vote of 1432 to 252.
And even (albeit more vaguely)
While discussing both the Munich Agreement and the Molotov-Ribbentrop Pact, Putin argued in 2009 that no policy could be seen “as reasonable and responsible if it trespasses moral and legal frames.”
Although as that article also explains, in the past few years, as Putin has rehabilitated Stalin, the MRP was also excused as (allegedly) driven by pure necessity. E.g., in a 2020 article that was sent to the Western press, Putin wrote:
The League of Nations and the European continent in general turned a deaf ear to the repeated calls of the Soviet Union to establish an equitable collective security system, and sign an Eastern European pact and a Pacific pact to prevent aggression. These proposals were disregarded. [...]
[The MRP] was done in the face of a real threat of war on two fronts – with Germany in the west and with Japan in the east, where intense fighting on the Khalkhin Gol River was already underway.
[...] there are many things the Soviet leaders can be reproached for, but poor understanding of the nature of external threats is not one of them. They saw how attempts were made to leave the Soviet Union alone to deal with Germany and its allies. Bearing in mind this real threat, they sought to buy precious time needed to strengthen the country's defenses.
Nowadays, we hear lots of speculations and accusations against modern Russia in connection with the Non-Aggression Pact signed back then. Yes, Russia is the legal successor state to the USSR, and the Soviet period – with all its triumphs and tragedies – is an inalienable part of our thousand-year-long history. However, let us recall that the Soviet Union gave a legal and moral assessment of the so-called Molotov–Ribbentrop Pact. The Supreme Soviet in its resolution of 24 December 1989 officially denounced the secret protocols as "an act of personal power" which in no way reﬂected "the will of the Soviet people who bear no responsibility for this collusion."
Now that CDJB has pointed me to the full text of the 1989 resolution, it indeed condemns the secret protocol, but you'll also note that the Congress passes the buck to Stalin (and Molotov) personally for it. (Below is machine translation.) Also, the main/non-secret text of the non-aggression pact is declared unproblematic.
The Congress of People's Deputies of the USSR hereby confirms that the non-aggression pact of August 23, 1939, as well as the friendship and border treaty between the USSR and Germany concluded on September 28 of the same year, as well as other Soviet-German agreements, are in accordance with norms of international law - became invalid at the time of the German attack on the USSR, that is, on June 22, 1941.
The Congress states that the protocol of August 23, 1939 and other secret protocols signed with Germany in 1939-1941, both in their method of drafting and in content, were a departure from the Leninist principles of Soviet foreign policy. The delimitation of the "spheres of interest" of the USSR and Germany and other actions taken in them were, from a legal point of view, in conflict with the sovereignty and independence of a number of third countries. [...]
The congress states that negotiations with Germany on secret protocols were conducted by Stalin and Molotov in secret from the Soviet people, the Central Committee of the All-Union Communist Party of Bolsheviks and the entire party, the Supreme Soviet and the Government of the USSR, these protocols were excluded from the ratification procedures. Thus, the decision to sign them was essentially and in form an act of personal power and in no way reflected the will of the Soviet people, who are not responsible for this conspiracy.
The Congress of People's Deputies of the USSR condemns the signing of the "secret additional protocol" of August 23, 1939, and other secret agreements with Germany. The Congress recognizes the secret protocols as legally invalid and invalid from the moment of their signing.
The protocols did not create a new legal basis for the relations of the Soviet Union with third countries, but were used by Stalin and his entourage to present ultimatums and forceful pressure on other states in violation of their legal obligations. [...]