It's inconsistent compared with alt-tab behaviour.
cmd-tab switches to the last used application (assuming you don't hold down), right now for me that switches from Firefox to Slack.
Pressing cmd-tab again switches from Slack back to Firefox.
However for window switches
cmd-` switches from my HN window to a jira window. cmd-` again switches to a webmail window. To switch from jira back to HN I have to press cmd-shift-`
cmd-tab switches to the last used application (assuming you don't hold down), right now for me that switches from Firefox to Slack.
Pressing cmd-tab again switches from Slack back to Firefox.
However for window switches
cmd-` switches from my HN window to a jira window. cmd-` again switches to a webmail window. To switch from jira back to HN I have to press cmd-shift-`