You can create a feature request and suggest what specifically to support. It’s up to Travis staff whether to actully support it though since they bear the maintenance costs.
AFAICS, libfuse3 is only available out of the box in Ubuntu since Disco. Travis is unlikely to support it because they only support LTS releases.
But for your task, you don’t really need a new environment.
- If your program needs to work in earlier versions of Ubuntu, install
libfuse3 from source and ship it with your app (either statically linked or linked as a private copy, e.g. via rpath) - If it doesn’t, run your build in a Docker container representing a newer Ubuntu (e.g.
ubuntu:disco). There, you can install the library viaapt.