Easily found with a basic web search"auto capitalize Google docs":

How to Stop Automatically Capitalizing Words in Google Docs
(if you want to turn it on, then simply check instead of uncheck)

and "auto captalize gmail," where all the returned items pretty much say this:

Gmail does not have auto-correct or even auto spell-check (only manual). While browsers have auto spell-check, they do not have auto-correct. So you’l need to find some browser extension or other utility to do that sort of auto-correction when composing messages.

Thank you for posting this question in the Chat Subgroup, as that's precisely where it belongs and sets a good example!

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Brian - Windows 10, 64-Bit, Version 21H1, Build 19043

You are not entitled to your opinion. You are entitled to your informed opinion. No one is entitled to be ignorant.

         ~ Harlan Ellison