If you have an issue when typing long text messages in Google Messages the issue is probably your font size. Reduce the font size in the message app and this issue may go away.
I had 2 Pixel 6a's one with the issue one without. On the one with the issue I tried switching WiFi between 2.4Ghz and 5Ghz networks, turning WiFi off, resetting mobile network settings, clearing the cache of the Messages and Carrier Setting apps, and restarting between each change. Still after typing a bunch of words, multiple enters between them to expand the text, the words would start to have a big delay between typing and showing on the screen. The only 2 other things different between these Pixel's was dark mode and font size in the messages app. I did the squeeze pinch just a little and the issue went away!
Hope this helps any others having this issue.