“Offered no evidence” is factually untrue
What’s the more plausible explanation - that a practically non-existent irrelevant-for-years terrorist group running unsophisticated operations in Syria suddenly assembled an A-Team to kill 150 people in Moscow, or that the Ukrainian citizen(s) who tried to flee to Ukraine committed the attack at the behest of Ukraine, which is currently at war with Russia? A real mystery!
Ukraine has done a lot of hopeless attacks in Russian territory with no real military aim, but with a stated purpose of maybe destabilizing society. So it's not a surprise that islamists turned ukrainian citizens and soldiers would carry out a terror attack in Moscow, if for no other reason than the fact that this isn't even the first time it happened. In the past, Zelensky has gone so far as to claim that the russians of Ukraine and Donetsk are so shook that Ukraine is already winning the psychological war. This was before the big offensive though.