They lowered interest rate on April when Ruble was 80/dollar. But Ruble became even stronger after

their central bank rate-cut move. I believe they will lower interest rate again soon.

You can trade ruble if you have business (export or import) with Russia. Ruble is linked with and backed by real economic activities. Given current sanction situation, that's good enough for Russia. Yes, if you make living by trading foreign currencies, ruble is not in your portfolios. But clearly Ruble is stablized. Biden's prediction is a joke.