Based on this image it seems that you have only one layer available.
You can’t ungroup / release / separate the sublayers if there’s no place for them to go.
It should work. Select your one layer by clicking on the circle on the right of the Layer Name.
Then from the panel menu, choose Release to Layers (Sequence).
It will look like nothing changed. However, you can now select all of the sublayers in one go and drag them down until you see a horizontal line. Release and the sublayers will now be layers of their own.
2019 iMac
3.6 GHz 8-Core Intel Core i9
64 GB 2667 MHz DDR4
Radeon Pro Vega 48 8 GB
Software OS 10.15.3
Adobe CC