While sales are definitely down (as always this time a years), to be fair, looking at your portfolio, you haven’t released anything new in almost two years. Sales will only go down for you. You can slow it down by at least updating all your items so any potential customers will see that they are not abandoned. Especially that WP theme of yours - you haven’t updated it for more than a year, no experienced buyer will buy that. Updating your items to comply with current WP requirements (more info here WordPress Requirements Update and New Gutenberg Optimized Attribute) is also a good idea to boost sales a little bit.