The traffic from Twitter had reduced a lot by now. In the evening I had Google Analytics opened when suddenly I saw dozens of users come from laravel-news.com. They had posted an article about the app (https://laravel-news.com/tailwind-css-online-code-editor).
I used this opportunity to make a Show HN post (https://news.ycombinator.com/item?id=20653942) and link it from the navbar of the app. This resulted in my submission reaching the front page of HN within an hour and 10 votes. After that I guess HN users really liked the app and I ended up being on HN's front page for 12 hours, peaking at #4.
I got over 5000 unique visitors over the next 48 hours and over 70 new signups.