I googled it for a second and this is what I saw " To convert GLSL to HLSL for Unreal, you can use SHADERed, which can automatically translate shaders and export them to HLSL. SHADERed can also be used for writing and debugging shaders."
Might be worth reaching out to the ShadeRed team and seeing if they could convert ISF. ISF is built off of GLSL. Most of the work that has been done is about converting GLSL shaders into ISF shaders, not the other way around. https://isf.video/
Also, depends on the shader you want to convert, sometimes the code has links to Shadertoy, so that’s the WebGL version.
I would ask ShaderRed if they support ISF shaders (and allow for cross conversion), or you could ask Unreal to support ISF, but I’m not sure how likely that is…