Stated within the discord before it's termination, @wagyourtail has been behind major advancements to Baritone's build system to allow Fabric to function with the official Baritone repository.
What this means is that, as of February 28th 2021 I began procedures to archive the remaining active portions of the Fabritone repo, which concluded earlier today.
For normal users, you should all be fine, as those who have installed via the marketplace should have been automatically upgraded to Baritone v1.6.3 (At time of writing, v1.6.3 is the latest release with Fabric Support). Those who have installed Fabritone manually however, are now obliged to upgrade to Baritone v1.6.3 as soon as possible, since support for Fabritone has been officially discontinued. API Developers will also need to manually switch over as well
Thanks for reading, and for any bugs related to Baritone, please report them to https://github.com/cabaletta/baritone/issues