The background blur property is still in beta and not fully supported by all browsers when viewing projects on Framer Cloud or on all Macs.
Some MacBooks will show artifacts in the background blur, most notably on MacBook Pro (2016 models) with a non-retina screen.
Background Blur + Blending Modes
In general, Framer does not support combining background blur with a blending mode. Note that if any layer in the hierarchy uses a blending mode, adding a background blur will create artifacts.
Previewing in Chrome
Google Chrome does not support background blur yet, so you will not be able to view projects with background blur on Framer Cloud in Chrome.
Previewing on Android
Android does not support background blur yet, so when you're previewing projects on Framer Preview for Android, the background blur will not render.