I am assuming this issue is related to running Sodium/Iris, however even in compatibility mode the issues remain. I have tried toggling almost every setting. In each of these images I have compatibility mode turned on.

immersive-portals-1.2.5-mc1.18.1
sodium-fabric-mc1.18.1-0.4.0-alpha6+build.14
iris-mc1.18.1-1.2.0-pre

Does the issue occur with BSL shader? Have you tried turning off motion blur?