Teams does both - normally it’s Enter to submit and Shift+Enter for a new line, but when you open the formatting tools it switches. They at least do have a message indicating which key combo inputs a new line, but it still gets me on occasion.

Slack is similar Shift enter in normal text. Enter in a code block, shift enter sends in a code block.

The Signal desktop app does both too, I guess, but in a way that actually makes sense. Enter sends a message since IMs tend to be short one-liners. Shift-Enter inserts a line break.

But if you click an arrow on the top of the text box, it expands to more than half of the height of the window, and now Enter does a line break and Shift-Enter sends. Which makes a lot of sense because now you're in "message composer" / "word processor" mode.