[1.16.4] Blur screen background

I want to create screen with blur background, similar to this mode. But I need it only for my own screen, not need to change vanilla. Faced a problem to found tutorial about this - all results in Google says how install shaders, how use shaders with optifine and e.t.c Can't found any one about how to use shaders in my own mode. Tried to investigate this mode, but it is old (last version support 1.13) and have tons of dark magic related to change vanilla screnes backgrounds. Also tried to investigate how vanilla use standard blur shader, but this is also so hard way (at least with my skills). So, does any one know tutorial, how to use vanilla or my custom shader at screen rendering? Or maybe exist some specific word, which specify - I need to use shader like developer, not like a gamer.