As @JCash wrote, as soon as Github adds ARM support to their CI (promised in the news by the end of this year), it will be possible to get a pre-built Defold binary for Linux ARM64. And probably to the cloud build server too.
P.S. In fact, it’s easy to build the engine from source, on Linux x86 at least. Plus, I described here how to cross-compile it from your x86 machine, for example.