Unlike the stable 1.8.8 version, Eaglercraft 1.12.2 is more complex. Because it involves decompiling more modern Minecraft code, GitHub repositories hosting these files are frequently hit with DMCA takedown notices.
Most players encounter an error saying they cannot connect to the server. This is rarely a game bug and usually a configuration issue within the index.html or settings.json file found in GitHub repositories. eaglercraft 112 2 github fix
Since direct links rotate constantly, use these search terms on GitHub to find the most recent "fixes": Eaglercraft-1.12.2-Service-Worker Eaglercraft 1.12.2 Mirror Eagler-1.12-Fixed-Manifest Unlike the stable 1
Look for "Full Asset" forks. Alternatively, you can manually upload your own resources.zip if the repository provides a "service worker" fix that allows local file injection. How to Find a Working Repository Unlike the stable 1.8.8 version