I don't know why the editor would crash after importing. This happens to me since Unity 2019.3 when importing any kind of package about 3/10 times. The only way to know why is to check the editor log, right after a crash, which you can find in C:\Users\<username>\AppData\Local\Unity\Editor\Editor.log If you can't find any Post Process Layer component, it means the Post Processing package hasn't been installed through the Package Manager. This is nothing to be alarmed about, but it effectively means you're choosing to use URP's built-in post processing framework, which uses the SRP volume system. You can use this setup guide instead: http://staggart.xyz/unity/sc-post-effects/scpe-docs/?section=setup-using-urp-2019-3. If you're past the installation screen, all the scripts for the URP will already be installed. An update for the package is running a little late, but this will fix the error in the fog shader. The reason is because this effect hasn't yet been ported to the URP. For now, you can simply delete the shader file.