Hi rosamundfrompoole
welcome to this Apple (user-to-user) Community
Am no expert in this area, yet your questions deserve some response.
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Re: Recently bought APP2 .... How can I use them just as hearing aids?
If available in your country or region:
You can: Take a Hearing Test with AirPods Pro 2 - Apple Support
and
Use the Hearing Aid feature on your AirPods Pro 2 - Apple Support
Else : Seems you always need a device to boost the incoming sounds.
Eg: you can use the iPhone as a microphone to better hear conversations
See: Use Live Listen with AirPods or Beats - Apple Support
Eg: Customize Transparency mode on your AirPods Pro
and Use Conversation Boost on your AirPods Pro
See: Customize headphone audio levels on your iPhone or iPad - Apple Support
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Re: I thought that I could use them to watch TV.
Seems you can with Apple TV: Use AirPods or Beats with Apple TV - Apple Support
or
Browse through this Third-party {non-Apple article for your brand of Tv: How to Connect AirPods to a TV:
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Resource:
AirPods User Guide - Apple Support
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More support . info. if needed:
AirPods Support Website: Find all the topics, resources, and contact options you need for your AirPods...
AirPods Support - Official Apple Support
All the best :-)