It doesn't have to be credible. It just has to be noise.
The West can push back. Here's a 2023 list of separatist movements within Russia.[1] Most of these are small and weak, but with outside support, pieces of Russia might be destabilized.
St. Petersburg/Leningrad oblast has potential, because it's close to Europe.
With Finland and Estonia both in NATO, access to St. Peterburg is available. The Russian military is rather busy with Ukraine, and there might not be enough troops available to quickly suppress an internal revolt.
The West can push back. Here's a 2023 list of separatist movements within Russia.[1] Most of these are small and weak, but with outside support, pieces of Russia might be destabilized. St. Petersburg/Leningrad oblast has potential, because it's close to Europe. With Finland and Estonia both in NATO, access to St. Peterburg is available. The Russian military is rather busy with Ukraine, and there might not be enough troops available to quickly suppress an internal revolt.
[1] https://www.aalep.eu/major-secessionist-movements-russia