From ChatBTC hope this helps.

While CoinJoin significantly enhances privacy, it is not completely anonymous due to several factors:

Detectability: CoinJoin transactions can often be identified on the blockchain because they typically involve equal-sized outputs or other recognizable patterns. This detectability can signal to observers that a privacy-enhancing technique was used, which might draw unwanted attention.

Anonymity Set: The privacy provided by CoinJoin relies on the size of its anonymity set—the number of participants in a given CoinJoin round. A larger group provides better privacy, but if the pool of participants is small, it may still be possible for an observer to make educated guesses about input-output correlations.

Heuristic Limitations: While CoinJoin disrupts common blockchain analysis heuristics, it does not completely eliminate all potential linking methods. Analysts might employ advanced techniques to infer information about transaction participants, especially if post-mix spending behaviors are careless.

Initial and Subsequent Transactions: CoinJoin primarily obscures the link between inputs and outputs within the same transaction. However, subsequent transactions that do not use privacy-enhancing techniques could potentially expose user identities or reestablish links between addresses.

Network-Level Observations: The privacy focus of CoinJoin is on-chain. Network-level observers could potentially gather metadata during the transaction process, such as IP addresses, which CoinJoin alone does not address.

Although CoinJoin improves privacy, users need to remain vigilant about their overall privacy practices, including how they handle coins before and after using CoinJoin, to maintain a higher level of anonymity [6][7].

Sources

[0]: https://gnusha.org/url/https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-March/020186.html

[1]: https://bitcoin.stackexchange.com/questions/107984#107987

[2]: https://bitcoin.stackexchange.com/questions/103252#103255

[3]: https://gnusha.org/url/https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-June/017976.html

[4]: https://gnusha.org/url/https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-June/017957.html

[5]: https://gnusha.org/url/https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-June/017958.html

[6]: https://gnusha.org/url/https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-June/017960.html

[7]: https://gnusha.org/url/https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-June/017961.html