@catcry160 That button is not used to activate onion skin but to see either drawings or adjacent frames relative to the current frame you’re viewing. To activate onion skin you have to use the buttons on the “display panel” or press the hotkeys O (previous frame) and ALT + O (next frame)
Also once activated to modify the onion skin parameters you have to visit the preferences by going to EDIT > PREFERENCES > TOOLS > Onion Skin