artist01

Thanks for sharing the link.
you can achieve this effect in Photo by adding 3 filters / adjustments to the text layer in masking position:
gaussian blur filter, set radius to taste Curves adjustment, select alpha channel, drag right node to the left ripple distortion filter, set radius to taste, and click with mouse to the point where you want the center to be Hope that  you have all the bits and pieces to get this working for you.

Thanks for confirming this @NotMyFault.
It would be nice if levels worked, but at least I can do it with curves, which is better than nothing.

What actually works best is a channels mixer adjustment, with alpha channel boosted to 200% (or as you like).
unfortunately there is a bug in Photo making levels unusable as nested layer (on alpha channel), but channels mixer works (nested to masking position!).
In Case you need a stronger effect, duplicate the adjustment layer.
add channels mixer adjustment  nest it to masking position of pixel layer containing text choose alpha channel increase alpha from 100% to 200% (or desired level) if you need more, duplicate adjustment layer once or multiple times
IMG_0059.MOV

Below a video and document to play with for understanding how threshold impacts color only, and a levels on alpha impacts blur radius. I copied the text layer and applied a gradient.
Another reading why grouping won’t help at all in this case: the group will “see” the underlying layers, so threshold is not limited to the text.

IMG_0058.MOV tutorial blur threshold alpa.afphoto

Unfortunately this will not work In this case.
the pixel layer with text has probably been created by applying Gaussian blur (destructively). the blur leads to all pixels becoming blurred, but only on alpha channel. The color is pure black for all pixels in that layer. (Both black text, and all invisible pixels with full transparency) the threshold adjustment works on color only, not on alpha. So it has no effect on the text layer at all. when on top, the lower layer will produce 100% alpha for all pixel in the canvas, thus the TH will start to work. The main question to @artist01 is what you want to achieve by your workflow, why blur and then use threshold? If you can explain what you want, we can show other ways to achieve this.
you could use a levels adjustment, select alpha channel, reduce white level. This will bring more pixels to full opacity, but keep the fully transparent. It depends on the radius of Gaussian blur if the result is what you want.

This is a "problem" in the sense that you dont get the expected result but this is how the threshold is supposed to work in this particular situation.
I believe that if you apply the threshold to the alpha channel you get the expected result.
You have to use a procedural texture for this (download at the end).

I think this is the best solution. But, I dont know whats going on because I can only do this with a curves adjustment.
The levels adjustment only works on top of the text and not as a child.
@NotMyFault, is your levels adjustment working properly?
ecco.afphoto