Re: "Accessibility read text iOS 18.1 does not function".
Wondering if you have checked the settings:
Settings > Accessibility > Spoken Content
Check it is "Speak Selection" that is turned on (ie: rather than Speak Screen)
Apple Support's online article for iOS 18.1 has all the tips:
Hear iPhone speak the screen, selected text, and typing feedback - Apple Support
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Re: "I am thrown out of the document altogether. I have no idea why is this would happen".
Could it be the main settings and the document settings are not in agreement as to "speak selection"?
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Re: "Any ideas?"
Your posted info. says "iPhone 8 Plus" ... yet if using iOS 18.1 you must be using a newer iPhone ?
Else: The newest compatible iOS version for iPhone 8 Plus is iOS 16.7.10
See: About iOS 16 Updates - Apple Support
If still using iPhone 8 you might want to check in Settings > General > Software Updates
(NB: If an update is available: It is wise to back-up iPhone data, before you update.)
All the best :-)