How can I copy entire chain of text messages (not just a single one) with the stock Android messages app?

How can I copy or export an entire chain of text messages (not just a single one) with the stock Android messages app? This is needed for a claim. I know I can screenshot stuff, but the date for older messages is missing. I know I can long press on a single message to select it. I can long press on multiple messages. But that's beside the point: how can I grab the data --- message, date & time received? If it's relevant, the phone is Pixel 4a.