Coverage chart / Kindle
Floodtide updates Kindle
Kindle comes from the Mac App Store, and Floodtide updates it in place. Here is exactly how it works, and the one thing it needs set up first.
How it works
Since 1.3.0, pressing Update on a store row updates the app where it stands: no App Store window opens, no password is asked for, and the row ends on the new version like any other. Update All includes Kindle alongside everything else. Floodtide carries its own copy of the tool that talks to the store, signed and notarised with the app, and runs it as you rather than as an administrator, which is why nothing is asked of you. It reads what the store is offering on this Mac rather than Apple's public listing, so a version your Mac is not being offered is never counted as an update you are missing.
The Floodtide installer has to be set up once, from Settings, before store rows can update in place. Until it is, the row says so and offers Update in App Store instead.
Kindle is not on the coverage chart because that chart is built from the Homebrew catalogue, and a Mac App Store title has no cask. The chart is not the whole of what Floodtide handles: the store is read live, on your Mac, from the same list the App Store's own badge counts.
What this says about the rest
MacUpdater kept a hand-maintained database of every Mac app, which is why it could claim near total coverage right up until the day it could not maintain it any more. Floodtide reads sources the vendors already keep current, so the coverage list is smaller and it does not go stale. The trade is deliberate: a shorter list you can trust beats a longer one you cannot check.
Questions about Kindle
Does Floodtide update Kindle?
Yes. Kindle comes from the Mac App Store, and Floodtide updates it in place. Since 1.3.0, pressing Update on a store row updates the app where it stands: no App Store window opens, no password is asked for, and the row ends on the new version like any other. Update All includes Kindle alongside everything else. Floodtide carries its own copy of the tool that talks to the store, signed and notarised with the app, and runs it as you rather than as an administrator, which is why nothing is asked of you. It reads what the store is offering on this Mac rather than Apple's public listing, so a version your Mac is not being offered is never counted as an update you are missing.
What does Floodtide need before it can update Kindle?
The Floodtide installer has to be set up once, from Settings, before store rows can update in place. Until it is, the row says so and offers Update in App Store instead. Setting it up is a single button, it is the same installer that handles updates needing an administrator password, and nothing about a store update asks you for one afterwards.
Does Floodtide hide apps it cannot update?
No. Floodtide shows an app it cannot handle with the reason attached, in the app and here. An updater that quietly omits what it cannot do is one you cannot use to answer the question "is this Mac up to date", which is the only question that matters.