This is a big reason why the Fabric versions are unsupported, because it's no longer practical to maintain them on its current state. This was not an intentional crash, and since QSL had long migrated to the Quilt Loader, I can't really do anything about it anyway.

With Fabric Loader 0.14.x, one of those hacks was broken, and therefore, the dreaded crash happens. With that migration, many of its code hacks used for running on Fabric could finally be removed, and so, they were. While at the time, I could carefully watch for any issues and eventually fix them through an update (a good example is an issue affecting Continuity being fixed on 5.0.0-beta.6), after 5.0.0-beta.6 happened, Quilt Loader was ready, and therefore, QSL has migrated to it. It ran on the Fabric Loader due to the Quilt Loader not being ready yet. On 5.0.0-beta.4, this resulted into the adoption of a JiJ'd Quilt Standard Libraries, which was needed in order to make a feature work. On the interim between the beginning of the Quilt toolchain's development and its release, Ok Zoomer was already adopting parts of Quilt that were ready at the time. Why is 5.0.0-beta.6 (the last Fabric version) not working on Fabric? If you attempt to run 5.0.0-beta.7+ on Fabric, this mod will warn you on startup about it through a carefully-crafted Fabric-only part of the mod, which will show a screen.

This means that all Fabric versions (including 5.0.0-beta.6) are no longer supported! I won't be able to fix any issues afflicting them. Since 5.0.0-beta.7, Ok Zoomer has completely switched to the Quilt toolchain! This will allow us to take advantage of its new APIs (such as its client tags system and its better config system) and in the future, will allow for much more (such as better key bind integration with Quilt Key Binds API). Ok Zoomer has migrated to the Quilt toolchain!

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