Hi nkfarlow,
Thank you for posting your question to the Apple (user-to-user) Community!
Re: "How do you turn off closed captions on an iPad when watching videos with Safari?
The option is there on the bottom right-hand corner of the screen, but nothing happens when I tap ‘off.”
You may have Closed Captioning turning on automatically on your iPad:
See if Settings > General > Accessibility > Media > Subtitles & Captioning is turned on.
If so: You may want to turn it off.
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Or ... If that setting was not turned on:
Wondering if your iPad's iPadOS software version is an earlier one than the iOS installed on your iPhone.
It is a good idea to keep all our devices updated to the newest compatible OS version available for that model.
You can always check if an update is available for a device: ie: Go to Settings > General > Software update.
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and / or If you are using any accessibility software on your iPad:
You may be able to adjust Safari settings in Accessibility settings.
Go to Settings > Accessibility > Per-App Settings.
Tap Add App, choose Safari, then tap Safari to adjust any relevant settings.
Hope there's something helpful to you here :-)