You can add a neon effect to your texts in Google Slides! And it’s super easy!
Go to Insert > Word art and write your text, hit enter. Customize your text font and then go to Fill Color and select a soft one, Go to border color and select its bright variant, select border weight and click on 3px (or more depending on the font you choose or the size of your Word Art).
Then go to Format options and select Drop shadow. Select the same color that you used for border and set 10% Transparency, 0% Distance and 50% or more for Blur Radius.
And that’s it!