I would have to agree with this, the behaviour of the new composer is strange and unintuitive when it comes to a simple thing like pressing return. Between this and a bunch of other immediate bugs that I’m trying to reproduce, I would have to say that this is a feature which doesn’t quite feel ready for prime-time yet. If the new composer were the default at the moment for example, posting on my site would be completely broken, as many times I’ll post images that I have hosted at Flickr.
I’m moving this to Feature since this is working as designed, though I understand this is not a design choice that you find desirable. We’re talking about this internally and will share more soon.
Please open new topics as you are able to reproduce bugs (and I would appreciate more information about what’s broken with the Flickr links); let’s keep this topic focused on the original poster’s comments.
It’s less common but we’re not completely alone in this, notion.so and medium.com work this way as well — generally the idea is to encourage more structure.
למי שמתעניין, למרות שזה לא מפריע לי באופן אישי, ההתנהגות הזו גם גרמה לבלבול אצל לא מעט אנשים בקהילה שלי שלא הכירו את קיצור הדרך של Shift + Enter (או שלא ציפו שיוכלו להשתמש בו).