Set g:zig_fmt_autoswitch to 0 in your vimrc to disable automatically switching to the location list if/when zig fmt encounters code formatting errors.
When set to 0, g:zig_fmt_autoswitch configures the Vim cursor to remain where it was prior to running zig fmt. The location list — which gets populated with code formatting errors as per normal — can then be viewed at a glance, without losing focus.
Either don’t set g:zig_fmt_autoswitch at all, or set it to 1, to keep the current behaviour of this plugin.