The bug
The blur shader is still used in Programmer Art and High Contrast, as well as other resource packs using opaque UI backgrounds. We can tell this is the case due to MC-268902.
How to reproduce
Open the debug menu with performance graphs via F3+2
Enable the Programmer Art resource pack
Observe how the graph at the left looks after unpausing the game
Expected results
The reported frames per second would not be lower when the game is paused.
Actual results
They are, implying the blur shader is being used even though it isn't visible.
How to fix
If the menu background nor the menu list background are found to have an alpha channel, it might be advisable to cancel use of the blur shader in a menu context entirely.
Alternatively, include a shader in Programmer Art that does nothing, and have it replace the blur shader.
Thank you for your report!
After consideration, the issue is being closed as Won't Fix.
Please note that this is not the same as Working as Intended, as this bug report correctly describes behavior in the game that might not be the intended or desirable behavior, but it will not be fixed right now. Sometimes, this is because the issue reported is minor and/or impossible to change without large architectural changes to the code base.
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