The sentiment in Washington before the Moscow attack was that Russians needed to experience firsthand the impact of the war in Ukraine. This attitude intensified as US sanctions proved ineffective, Russian advancements in Ukraine quickened, and President Putin received a high level of support from the Russian population during recent elections.
Previous attempts to make Russians understand the war's effects included drone strikes on major city centers, attacks on infrastructure, and efforts to destabilize Russia's economy.
https://www.csis.org/people/emily-harding
Disclaimer: I haven't followed this particular story very closely.
ISIS-K and American Intel have connections to say the least. It's plausible that a terrorist attack claimed by ISIS-K is also a CIA thing. I would not be surprised to find that some of the people there trained in Syria/Iraq and were active in Afghanistan. I wouldn't be surprised if there were a mix of people with similar backgrounds but different nationalities cobbled together for this relatively recently.
This is all speculation on my part of course. Just saying what wouldn't surprise me.