To be honest, I'm surprised that someone using SQLite would try to access it directly from multiple threads or processes without fear of data racing.
https://sqlite.org/faq.html#q5
One writer, multiple readers is a specifically supported way of using SQLite.
Why should you be worried if it is used as designed?
Well this whole article is about a company discovering a catastrophic corruption bug even though they were using it as designed.
I think the lesson is that if you're ever actually worried about concurrency then just don't use sqlite. We can see here that concurrency is hard and the bugs are old and deep.