I posted the wrong link. As I can’t edit my previous post, here’s the correct link:

https://artemis.phoenixart.com/

So, one solution I found is to wrap the paragraph within a Span, and assign a 100% width to that.

This works because in order to keep the text left-aligned, the Gutenslide block needs to be filled. If there isn’t enough text to fill-up the entire block, the text stays centered.

It seems this could be improved.