You can’t do blur in widget using normal nodes as blur effect requires looping which material graph don’t support (well you could do it but it would be gigantic node spaghetti), so custom node is only way, you can find many hlsl examples for blur you could use. The lest post on thread you posted shows code that works in 4.21, if you have any issue then explain what does not work, as we can only guess without any info from you.
But there interesting alternatives you can use:
-There background blur widget in UMG, which you could integrate with HUD and make it cover entire screen and use it as post process, but i not sure if there any performance impact on that as this will run on slate renderer, but considering blur still runs on GPU it should not be much of a issue
-You can use build in Depth of Field effect in post processing, as essentially it is just distance ranged version of blur. Set to GaussianDOF method, Focal Distance to 1 and Focal Range, Near and Far transition to 0. After that you can control streaght of blur with “Far Blur Size”. Ofcorse this being DoF it is most likely more expensive then normal blur shader.
Hey. It was me posting that piece of code a few hours ago. Did not know fixing would be that easy. Reading the SceneTexture properties changed a bit and also screen uvs in hlsl. Anyways. Thanks for your answer