Decades ago, Return and Enter were two different keys for that reason: Return to insert a line break, Enter to submit your input.
Given the reduction to a single key, the traditional GUI rule is that Enter in a multiline/multi-paragraph input doesn’t submit like it does in other contexts, but inserts a line break (or paragraph break), while Ctrl+Enter submits.
Chat apps, where single-paragraph content is the typical case, tend to reverse this. Good apps make this configurable.
Given the reduction to a single key, the traditional GUI rule is that Enter in a multiline/multi-paragraph input doesn’t submit like it does in other contexts, but inserts a line break (or paragraph break), while Ctrl+Enter submits.
Chat apps, where single-paragraph content is the typical case, tend to reverse this. Good apps make this configurable.