It’ll work but it won’t be ideal. It depends on what you want to do. Utility programs tend to use features that game engines don’t provide (file-system stuff, communicating with the OS, communicating with hardware, etc.). Of course you can make native extensions to add features, but that’s not really different from learning kotlin or java and android studio…
Utilities tend to be more UI-heavy than games too. (Not that this will change, whether you use Defold or not, just something to be prepared for.)
Last I checked there was no way to make the engine go “idle”, I asked the same question a while ago, but I agree about trying to dynamically change the frame-rate like Pkeod says, I never tested that thoroughly myself.