[Late Update] The fish 3.5.0 release is not responsible for my tmux issue. False alarm. Downgrading did somehow help me regain shell interaction, but I can't

[Late Update] The fish 3.5.0 release is not responsible for my tmux issue. False alarm. Downgrading did somehow help me regain shell interaction, but I can't create a new session/pane, etc. I think something else broke my tmux setup during the brew upgrade, or possibly even before it.