It has the bubbles around what each person says, which is the style that many of the chat apps in your link have as well. OK, they are flat bubbles now rather

It has the bubbles around what each person says, which is the style that many of the chat apps in your link have as well. OK, they are flat bubbles now rather than shiny blobby ones, but it's the "bubble for everything someone says" that makes it look dated. I hated the "bubbles" look back then and always used themes that just presented text as text, with possible unobtrusive delimiters between people's comments. Like Slack and Discord do.