ModUpdater is a Fabric mod to help keep other Fabric mods up-to-date. It should be relatively simple to get it working for FastFurnace by adding a handful of lines to the fabric.mod.json file, although I canʼt actually find where that file comes from in this repository.

This is not a fabric mod

Thank you for the quick reply even when the issue was nonsense. I got confused because somebody ported it to Fabric at https://www.curseforge.com/minecraft/mc-mods/fast-furnace-for-fabric; Iʼll open an issue with them instead.