There is a Ring Signature implementation in C++ by Libbitcoin team. We can find the details in the following GitHub repository. Is it feasible to use Monero like Ring Signatures together with the CoinJoin Technique in Bitcoin without a soft fork on the core protocol.
Using ring signatures off-chain to form a coinjoin transaction sounds hard, especially since because BTC doesn't have ring signature support without a hard fork or a soft fork.
You may find Cashfusion, an instance of CoinJoin shuffling, interesting, it's fully applicable to BTC and it uses TOR, which is simpler than Ring Signatures.