Logs: https://mclo.gs/ujWEy0w
The only mods are Fabric API and Blur+

I also had the same error in the development phase of my Modpack LifeMC and apparently I thought maybe Satin API instead is Blur+

This is due to the new blur radius config option. For now, downgrade to v5.0.2.

I recommend to mark it as alpha or beta and not release.

I have not been able to replicate this on my side, but it was a rather easy fix.