Using fullscreen mode for splited window • Tuan Tran

tl;dr: Zoom the pane with <prefix>z or resize-pane -Z.

The default function for <prefix>w is choose-tree -w (version 2.6+; in older versions it was choose-window). These are displayed in the pane, so zoom the pane to fill the window temporarily.

Combining the two operations on a single keybind should be fairly straightforward. This can go in your .tmux.conf or into a running session (<prefix>:):

# replace default window-chooser: zoom first
bind-key -T prefix w resize-pane -Z \; choose-tree -w

See man tmux:

choose-tree [-GNsw] [-F format] [-f filter]
            [-O sort-order] [-t target-pane] [template]
    Put a pane into tree mode, where a session, window or pane may
    be chosen interactively from a list. -s starts with sessions
    collapsed and -w with windows collapsed. [...]

Ref: https://unix.stackexchange.com/questions/417853/tmux-interactive-window-selector-fullscreen-while-in-split/417884#417884