We have seen some confusion about the KiCad release candidate announcements and how they differ from nightly builds, so there is a new page on the website that hopefully clarifies things:
TL;DR: KiCad release candidates are the same as nightly builds, just with a different number. Users testing release candidate builds should treat them like nightly builds, and continue to upgrade to newer nightly builds during the release candidate process.
Users who install KiCad via some process that delivers updates automatically (for example, a Linux package manager) should pay special attention to what is going on during the KiCad release candidate process, because when 7.0 final is released, users who have been testing KiCad release candidates may want to switch from using nightly packages to stable packages, as the nightly builds will immediately switch to version 7.99 and start receiving new features that may break compatibility with 7.0. Users running Linux and installing KiCad through a package manager cannot in general run two stable versions at the same time, for example 6.0.11 next to 7.0.0. If this is desired, our recommendation is to use FlatPak for one of the versions.