I have no idea why open source projects would want to use illustrations with this big tech corporate artstyle in their apps and documetation pages.

They seem to get them from https://undraw.co

Deej-Ai is pretty cool. It uses a model based on scraped Spotify data and can automatically generate playlists. https://deej-ai.online

Plus how would you want to exploit a F-Droid SQL injection vulnerability in the search bar?

AFAIK you cannot trigger searches using URLs, so the user would have to type/paste the SQL into the search field themselves to mess up their database.