Text Thread
Can I download and print a long series of text messages?
iPhone 11 Pro, iOS 14
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If you have a Mac: see this Apple articles below:
How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac
https://support.apple.com/en-gb/HT208386
You can take a screenshot and print it out.
From the Mac, you can just copy and paste the text into Pages then print it out.
Finder -> Apps -> Messages -> select a messages -> copy -> paste to xxx.
If you have multiple messages, you must select, copy & paste per message.