We have moved our forum to GitHub Discussions. For questions about Phalcon v3/v4/v5 you can visit here and for Phalcon v6 here.

Where are the phalcon old documents?

2.1.0 was never relased. Basically just use latest docs. Or maybe you meant 2.0.x ? https://docs.phalcon.io/en/2.0.0/