I’m surprised no one has mentioned pdsh yet. Piped to dshbak and output was grouped by response. I’d probably use a config management tool for anything more than simple commands now but that tool was indispensable for managing our fleet, when we used to actually connect to machines.
To collect all the results and show which ones are the same or different, use dshbak (i.e., "pdsh <parameters including servers>|dshbak"): https://linux.die.net/man/1/dshbak
Similar things, sometimes more convenient but less efficient for a large number of servers, are to use the konsole terminal program and link multiple window tabs together so the same typed command goes to all, and quickly view the results across the tabs; or to use tmux and send the same commands to multiple windows (possible useful "man tmux" page terms: link-window, pipe-pane, related things to those, activity, focus, hooks, control mode).
And others that I haven't used but which also look possibly interesting for platforms where pdsh and dshbak might not be available (like OpenBSD at least):
