It is possible to open an image in Expert mode and click the fx button at the bottom of the window. Choose painting from the pull-down menu. The middle thumbnail is for the oil painting effect. Double-clicking will apply the effect to your image. If the effect is too strong you can go to the layers tab and change the layer opacity.
Another method is to select the smart brush which lets you choose an oil painting effect. You then use the smart brush to select parts of the image where the effect is to be applied.
This video relates to an older version of PSE but the tools are available in PSE 2018.
A guided edit is also available in PSE 2018 for making a water color effect.
You can find it in the Effects (fx) panel, under the Painting dropdown menu. It is the middle choice. I would recommend applying it to a new layer and modifying the opacity. Otherwise, it can be very blotchy.
You can also use the Guided Edit>Fun Edits > Painterly guided edit.
That was odd. When I first opened this conversation, I only saw the OP with no response.