How do you react if a competitor appears outta nowhere?

Hi Dominik,
I would say don't worry about it much. Here is a similar thread and my comment on the topic: https://www.indiehackers.com/post/i-built-project-for-6-months-and-just-now-discovered-an-existing-competitors-project-which-is-better-than-mine-666c3a260b?commentId=-MTXEQDRCO76eBIED9mD

Not sure if I'm the most qualified but after looking at the design of many products I realized that despite two products seeming exactly the same they can fill totally different roles.

This article is pretty good at showing that: https://m.signalvnoise.com/position-position-position/

ignore them