Ok but on Tesla Software Updates - Not a Tesla App it's appearing also
Same trust-level. They always post at the beginning of the week with the comment "Release notes are not yet available". Teslaversion tries to sell some software, "Not a Tesla App" tries to build up a community. So it's really just asking for attention.
Most reliable source is still TeslaFi.com Firmware Tracker and there is still no mention of 2021.4 on their twitter https://twitter.com/teslafi