Turns out, VSCode true is set to "explicit" since VSCode 1.85.0. It seems boolean values were supported until 1.84.0.
References
https://code.visualstudio.com/updates/v1_85#_code-actions-on-save-and-auto
https://code.visualstudio.com/updates/v1_83#_code-actions-on-save-and-auto-save