URP 14.0 incompatibility
This could be a 2022.2 beta issue that's a Unity bug, I have no idea—not familiar enough with this implementation to know. But, I've tested URP 14.0.3 with Unity 2022.2.0b4 and the outlines do not render, and instead each outline mesh causes an extreme amount of lag. Taking a peek with RenderDoc it seems the meshes are rendering as overlapping full-screen triangles, a huge amount of overdraw, and a buffer that's usually present for the positions is not there. Hopefully that helps.
I fixed the issue by replacing OutlineColor.URP with a plain white unlit shader made in Shader Graph.
Ran into the same issue and as with @vertxxyz I sorted it by creating a new shader that just renders solid white drawing on the backface