While it’s always possible that Amazon has accidentally broken the compatibility with third-party launchers, this seems a little unlikely. The Seattle-based company has released a slew of new software updates for a range of hardware, including Fire TV OS 7.2.7.3 for the Fire TV Stick Lite, Fire TV Stick 4K Max, Fire TV Stick (third-generation), and Fire TV Cube (second-generation), Fire TV OS 6.2.8.7 for Fire TV Stick 4K, Fire TV (third-generation), and Fire TV Cube (first generation) and Fire TV OS 5.2.8.7 for Fire TV Stick (first- and second-generation) as well as second-generation Fire TV.
Given that all of these versions of the software bust compatibility with third-party launchers – it seems unlikely that it’s a mistake.
Amazon isn’t the first company to break homescreen replacements on its hardware. Huawei, which previously relied on open-source Android to power its own streaming set-top boxes, has locked down the ability to replace its software with a third-party alternative. Google’s own Chromecast with Google TV also limits how effective these launchers can be. So, Amazon isn’t doing anything out of the ordinary here.