Elementor is one of the best WordPress website builders around with plenty of add-ons that extend its capabilities. The Image Comparison Plugin for Elementor is a nifty script that lets you showcase before & after photos on your site. It supports vertical and horizontal orientation and should work with most themes on the market.
You can customize before & after label, border, radius, padding, and other options. The label can be removed altogether. Jewel_Theme is just the developer behind this plugin.