I think I discovered a keyboard shortcut error in Safari. On the menu/Window, the shortcut for switching tabs shows:
However, using the Control key does not work but using the Command key does.
Please verify and tell me I’m not crazy! 
Assuming I’m right, how does one inform Apple?
Ctrl-Tab and Shift-Ctrl-Tab work as documented on Safari 15 on my M1 MacBook Air running Big Sur.
But you’re not crazy. Something else is going on. Cmd-Tab should bring up the app switcher.
Not tab, shift-control-right/left arrow for switching tabs in Safari. That does not work but that is what shows in the menu. What works is shift-COMMAND-arrow key.
Command Tab does switch apps.
Your illustration shows the Tab key. And that’s what works for me.
I also have “Use keyboard navigation to move focus” checked on the Shortcuts tab of the Keyboard System Preferences.
I apologize, either I’m missing something obvious or I’m not being clear. I’m referring to the shortcuts in Safari for switching tabs in Safari.
In Safari’s menu/Window, the shortcuts are as shown above, which shows the CONTROL key as a trigger but this doe not work for switching tabs in Safari. But, using the COMMAND key as a trigger does work.
As to keyboard shortcuts in system preferences, I think that is a different issue.
Am I missing something here?
Ditto here. There’s nothing wrong with the shortcuts shown in the OP’s image.
I assume there is some other conflict on the OP’s machine that has nothing to do with Safari. Easy to check. Quit everything and boot into a different or new user account and see if Safari there behaves as expected. That’s always the first thing I do before reaching for the phone.
Yes.
is Tab, not the arrow key.
Well now, that explains it! Apologies to @karlnyhus. Sorry for being a Goober on this! Good thing humility is a virtue because I just got a dose.
⌘⌥→ and ⌘⌥←
(Command+Option+arrow left or right) work too. It’s more intuitive for me.
YES, that is much easier to reach with one’s fingers, thanks!
I often imagine engineers sitting on a beach having a drink and comparing notes about what they’ve done to users in the past.
Engineer 1:
When I worked on Safari, I made the next tab shortcut control + tab! lol
And get this - previous tab is control + shift + tab!! Muwahahaha
Engineer 2:
Wow, that’s awesome! I’ve put a number of support structures in front of screws that people need to remove during servicing equipment, but nothing as devious as that!
