Run screen in UTF-8 mode. This option tells screen that your terminal sends and understands UTF-8 encoded characters. It also sets the default encoding for new windows to ‘utf8’.”
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Same as the ‘utf8’ command except that the default setting for new windows is changed. Initial setting is on if screen was started with ‘-U’, otherwise off.”
Screen does not have UTF8 support, tmux does.
Otherwise just a bunch of more sane original defaults in tmux to make things much familiar.
In 2026 if given a choice between screen and tmux to use/learn, most are going to go with tmux.