None of these are idea:
The pdf reference manuals are versioned per release, but generally we only link to the latest: https://www.freertos.org/Documentation
The History file will tell you when features and API functions were introduced: https://www.freertos.org/History.txt and https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/master/History.txt
API functions on the FreeRTOS.org site will often say the version they were introduced in.
The source files for any given release also contain the documentation - for example see https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/master/include/task.h#L239