Safari on iOS 17.6.1 reports it's user agent as Safari 6 on iOS7

Where are you seeing it reported as Safari 6? If you are using iOS 17.6.1, you have the latest release of Safari. There are Safari Extensions that you can install that will change the User Agent, so if that is the case, then remove the Extension.

And do you have any Safari Extensions installed at Settings > Safari > Extensions?

What about any Profiles at Settings > General > VPN & Device Management?

I have reviewed the few reports that I have been able to find, but did not come up with a clear solution. I also understand you do not want to do a clean install and don't blame you if that can be avoided. I would try these steps:

• Force Close Safari by slowly sliding up from the bottom of the screen to about the half way point to bring up the App Switcher. Find Safari by swiping left if it is not the top most app and swipe up on it to close.
• Go to Settings > Safari > Clear History and Data, and confirm.
• Force Restart your iPhone - This may take a couple of attempts to get the speed and sequence correct and the last step of holding the side button until the Apple Logo appears could take up to 15 seconds. Ignore anything else you see on the screen during that time until the Apple Logo appears. If you do not see the Apple Logo start over and try again.

Force restart iPhone - Apple Support

• Check the browser again using this site instead to see if the results are different.

https://www.useotools.com/what-is-my-browser

Gene5is wrote:

Many websites cannot be used correctly with Safari, and I am getting prompts that this version of Safari is no longer supported.

The reason is that those sites are still using an outdated and privacy-intrusive "user agent check" to determine browser compatibility.

Refer to this excerpt from Apple's Safari Developer Documentation (emphasis added):

Important

Use feature detection to enable or disable functionality instead of relying on the name or version of the browser in the User Agent string. Learn how to detect available features on MDN…

The passage regarding feature detection in that document uses even stronger language:

"... this is a terrible practice that should be discouraged at all costs."

It goes on to describe how that feature is "ultimately pointless," and the pointlessness is manifesting in your frustration.

As far as that is concerned, all my iPhones are reporting the correct "user agent" if I use the first website you cited (whatismybrowser). On the other hand the second website you cited (useotools) reports results similar to yours. Both Brave and Firefox are reporting it as Safari, which is of course wrong. Same iPhone, etc. Yet you are reporting different results.

If for no other reason this example illustrates the futility of using the "browser sniff" code that's causing you trouble.

What to do about it... you already ruled out Safari Extensions and VPNs, and I don't use any either. Yet x.com works fine. Will resetting your iPhone fix things? I doubt it. Before you do that try resetting its network settings: If your iPhone or iPad won't connect to a Wi-Fi network - Apple Support. Step 7. If that doesn't help (and I doubt it will) then proceed as described under Get more help. Let us know what you find out.

Sorry I don't have an explanation or solution for the wrong user agent being reported. It does look like you are going to need a Factory Reset. Hopefully you are using iCloud Photos where those will be redownloaded to your device even if you are unable to restore from a backup. In most cases, your Contacts are also in iCloud so it should not affect those either. It is true that third party apps will need to be downloaded and any data that those apps stored on your device would be lost.

Please follow up if you are able to discover any additional details that could have been the source to the problem.

Thanks for jumping in. As you, I was unable to confirm the results the OP had using Safari on 2 phones with different iOS versions and was unable to explain why that would be happening. I agree that sniffing the user agent is not reliable, but the site the OP used correctly identified Safari and iOS version on both of my devices, so could not determine what may be different for the OP.

Thanks for the update! Sometimes we just don't know why a problem occurs, but knowing a solution that works will hopefully help other users who may have this same issue. Your contributions and troubleshooting steps you took are appreciated.