cadenas
Encrypt a file with a password, right in your browser
...It uses Argon2id and XChaCha20-Poly1305, detects any change to an encrypted file, and can read and write the age format, so files stay readable with other tools. The same tool comes as a command line for Windows, macOS and Linux, a Docker image you can self-host, and a JavaScript library.
cadenas is free software (MIT) with a documented file format. It has not had an independent security audit yet; the threat model and format are public for review.