Tmux is available as a module instead of through an rpm.
$ module spider tmux
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tmux: tmux/3.0a
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You will need to load all module(s) on any one of the lines below before the "tmux/3.0a" module is available to load.
gcc/8.3.0
Help:
Tmux is a terminal multiplexer. What is a terminal multiplexer? It lets
you switch easily between several programs in one terminal, detach them
(they keep running in the background) and reattach them to a different
terminal. And do a lot more.
You should be able to access by running module load tmux. We’re trying to minimize use of rpms and making it available as a module allows the user support team to maintain it which should improve responsiveness to issues.