Here is a way to do the frequency separation using the High Pass filter. The advantage (over the more advanced Apply Image method) is that you can visually see the radius that is right for your image. This method also works the same no matter if the image is 8-bit or 16-bit.
If you have no idea what I am talking about, here are some good links:
(I also made an action that you can download and use.)
1. Create two merged layers and name one “Low” and one “High”.
2. Select the High layer and open Image>Adjustments>Brightness/Contrast…
3. Check “Use Legacy” and set Contrast to -50. Click OK.
4. Open Filter>Other>High Pass… and select a radius that shows the texture you want to separate (Remember the radius value, we need it later.)
5. Change High layer blending mode to “Linear Light“
6. Select the Low layer and open Filter>Blur>Gaussian Blur…
7. Enter the same radius value you used in the High Pass dialog and click OK.