Right, I’m not completely sure about this, but I think there was no blog post about this. But it was mentioned in several or relay operator meetups and in the forum. See [tor-relays] PSA: Tor 0.4.7 reaches end of life (EOL) on 2024-01-31.
Actually, if you look closely, step two is about configuring Tor’s project repository, which will always have the latest version available. Additionally, the guide you get redirected to in order to configure the repository, mentions the backports for armhf processors.