Sri Lanka is bankrupt and doesn't have any forex reserves. On the other hand, forex reserves of Russia is one of the largest in the world, and they have enough funds to make the interest payments. These two countries can't be compared side by side, as the situation is entirely different. One similarity that I could notice is that the ruling class is extremely corrupt in both the cases. But at least in case of Russia, the rulers have made sure that their corruption won't result in the total bankruptcy of the country.
Regarding the default. This is how international sanctions work. Even if Russia can pay this amount, but the sanctions have made it such conditions that it cannot do it. Sanctions are designed to make sure that the aggressor does not feel free in this world and put pressure on him in any non-military way so that he stops the war he unleashed in Ukraine.
LOL.. this is what you got? A few forest fires raging in Siberia is the sign that Russia is bankrupt.